I've actually posted about this midway through 2021 and I've gotten lots of helpful advice and I definitely need some more.

I have a 2003 Dodge Ram 1500 5.7 and I've been chasing this noise that occurs intermittently in my engine for a few years now since I've had about 228,000(?) miles on the truck, somewhere around there. I have 253,000 miles now on the old girl.
I have no idea what is causing this noise and I've done quite a bit of work trying to chase this down. I have a video of the truck making this noise and one where it doesn't (it's hard to pick it up on video and sometimes when I try to record it doesn't do it, almost like it knows or something) Its not like a knock or a tick, it's more like a rattle, it sounds like a humvee diesel while idling.

-Here's what I know about this noise:
-No check engine light, truck runs perfect.
-It only makes this noise at idle, the sound will speed up a little bit with the engine revolutions and goes away after like 800 rpm, then when I let it idle down it'll be quiet and after a few seconds it sloooowly comes back. It doesn't seem to really go away on it's own.
-It doesn't matter if it's hot or cold idle, nothing seems to really decide when this noise happens but if I idle it long enough it shows up and often just doesn't go away until I rev or drive the truck.
-It doesn't make the noise right at startup, but after about a minute of idling it'll show up.
-I'm absolutely sure it's not lifters or cam, and I'm almost absolutely sure it's not rod knock (even though sometimes it gets loud and sounds like it's about to sling a rod)
-If I drive around for a long time (about an hour+) and hot idle it, it's completely gone, but if I idle long enough (several minutes) it slowly starts to creep back.
-I can't tell exactly where it's coming from but it sounds louder underneath the truck.

-Here's what I've done trying to solve this noise:
-I've talked with a mechanic and he said that it's normal for these hemi's to make these noises and that he had a 300 that made the same noise. My moms 2010 Ram 5.7 doesn't make this noise at all though and sounds buttery smooth (although it has a stock exhaust)
-I have torn the engine down to the block and I pulled out the cam and lifters, all of them were astonishingly perfect, they had zero wear or blemishes and looked like they were perfect. The cam had zero wear. I put the cam back in and replaced the lifters anyway (OEM from the dealer) in addition to the pushrods (also OEM), which were also perfect minus just some oil staining. Cylinder bores looked pretty dang good, wear was even, cross hatching was still visible and there were no scratches or anything out of the ordinary in the bores.
-I replaced the timing chain, gears, and guides (OEM from dealer) and they were in excellent condition berfore changing.
-I replaced the oil pump with a Melling High Volume pump on reccomendation from several sources.
-Exhaust manifold bolts and gaskets, the bolts were pretty rough and the back ones were all broken.
-Replaced every gasket involved in the process, timing cover, head gasket, intake gaskets, truck definitely ran better after, still makes the noise tho.
-I pulled the transmission back and inspected the flexplate and torque converter and hardware, to the best of my ability from underneath the truck in a driveway, there were no cracks or damage or loose bolts or nothing wrong to the eye.
-I dropped the oil pan and inspected the rod bearings and main bearings, they all had moderate wear and I decided heck with it and rolled in some bearings with plastigauge and the clearances checked out perfectly (242,000 miles)
-I had an oil analysis from blackstone at 243,000 miles with 1,635 miles on the oil and they quote "Universal averages show normal wear from 5.7L Hemis after about 5,900 miles on the oil and your wear levels are very low comparatively, even with the shorter interval in mind."
-I did a compression test and every cylinder had almost perfect factory compression readings minus one that was maybe 5-8 PSI lower.
-Don't know how good of a test this is but when I was in the oil pan I pulled and pushed on the rods to see if the wrist pins might be tight or have play in them and they seemed just fine.

Nothing seemed to work and most people I brought it to and asked about it either couldn't help me or claimed it was "normal", is that true??? The truck makes tons of power and used to be my stepfathers truck before I bought it from him at 180,000 miles and we've all religiously changed the oil around 3,000-3,500 miles, I do know he changed the valve springs and seals shortly before I bought it. Revs smooth as silk and only makes this noise when sitting and just idling. I'm determined to keep this truck because it's my last real memory from my stepfather since he passed away and I'm not afraid to get dirty to keep it healthy. The transmission was replaced with a reman around 225,000 miles when I was in the military due to the torque converter going out and wiping out the trans (my fault), if that's somehow relevant.
I've been all over the internet searching and I found one video where a guy had a bad flexplate and it made the exact same noise as my truck and he had a bolt loose and it was cracked but mine seemed perfect, I got photos of the bolts and mounting points and they seem fine. Is this possibly piston slap? The bores in the cylinder look very even and clean and I can still see cross-hatching present throughout the bores. Sometimes the noise is very loud and sometimes it's very quiet and you can barely hear it, if I just started the truck it's not there but it slowly creeps up, then sometimes it just stays there or it'll go away, and then come back again and then it just keeps rattling without stopping until I drive the truck or rev it up a bit.

This is an old video from 2021 but it captures the sound perfectly, it's the loudest after 15 seconds in.

This is current as of last night but it's recorded with a crappy phone and it wasn't that loud then, but you can hear it especially towards the end when I'm under the truck. It doesn't help that I have a bad muffler now with an exhaust leak halfway down the exhaust as well.

Recorded with the same crappy phone but this is when it isn't making the noise.. for reference I suppose


I apologize for the lengthy post, but I'm hoping I can get some guidence or advice here, thank you everyone for reading this and thank you for any help you can provide.

 

From the first video, it sounds like the hemi tick to me. This is a general term that covers noise coming from either fuel injectors, exhaust leak, or valve lash.
Get a mechanic's stethoscope, or 2 ft length of garden hose, and put one end on an injector and other end on your ear. If that's not the source, listen around the header/cylinder head area.
Since noise goes away when warm, more likely source is the header or valve lash. But hemi injectors are notoriously loud.
Also check engine and tranny mounts. I think not likely a mount, but worth checking.

 

I've tried the hose method and it was pretty inconclusive to be honest, I can't really seem to find where it's coming from whether I check around the oil pan or the exhaust manifold, I thought it it might have sounded louder at the back of the manifold but I couldn't be sure, and I've replaced the manifold bolts and gasket and it didn't change anything. The injectors are all clicking away very quietly and I know for sure it's not them because the noise is 100% coming from the bottom somewhere.
Also it doesn't matter if the engine is hot or cold, it still rattles away anyway. I could live with it if it went away when it was warmed up.
Engine and transmission mounts are fine.

Edit: I have a 2010 Ram that has a definite exhaust manifold leak and it sounds different, also goes away after 20 seconds and never gomes back, so I'm pretty sure it's something else, although I'm planning on going to an exhaust shop to have the muffler replaced maybe I can ask them to check as well.

 

Did you check crankshaft endplay when you were doing the bearings?

 

Actually no, I did not. How would I go about doing that? Do you think it could make that noise?

 

It could be a root cause, not an easy thing to do since you've re-installed the engine.

Have you pulled the serpentine belt and (briefly) run w/o that load to see if the noise is still present or different?

Its possible that that something with the converter or trans pump is causing it too. Have you checked at idle with the trans in different modes (P, R, D) to see what happens with the noise?

 

The noise is there in all different gears/modes, only when the engine RPM is at idle. I can try pulling the belt and seeing if the noise is still there but it sounds more like it's towards the back of the engine bay area underneath, unless you think the belt pulling on the harmonic could be causing that if there's end play? I also don't really have the equipment currently to pull the motor due to being at school so hopefully if there's a fix I can do it with the motor still in, I can drop the oil pan pretty easily since it's a 2wd.

Edit: just checked, still makes same noise with the belt off

 

Is it possible that the exhaust manifold is warped and that even though I cleaned it up and used a fresh gasket and bolts that it's still leaking bad? It wouldn't make sense to me due to how the noise behaves but maybe it's plausible?

 

Betl/Trans test.... I was looking at eliminating some potential sources.

if the exhaust manifold is leaking, you should see some evidence. Usually one would put a straight edge against it when its off, so you can see if it needs to be flattened. If you have a leak before your o2 sensors, you might be able to see fuel trims reacting to that condition. Early hemi engines did have a somewhat chronic exhaust manifold problem, and I have heard of people saying they needed to mill/sand them to get it to mate with the head.. When you replaced your exhaust manifold gaskets, was it obvious to you where it was leaking? If so, look at that area again.

 

Thank you for the reply and advice, I appreciate it. When I had it off there were some broken bolts and a small carbon deposit on the head around one of the broken bolts and I cleaned it up but I didn't check the surface all that well nor think about it besides cleaning it, I'm definitely still just a monkey with a toolbox lol and I'm still learning. I haven't seen any more carbon there but I'll check it out again. Maybe I can use this as an excuse to throw some headers on.