To tell you the truth, I had a similar sound on my 98 for years. Never figured it out, and didn't worry about it much actually.

 

chalk me up to having the same noise in my 99 1500 5.9 4x4 as well. doesn't annoy me too much as i have the radio blaring most of the times

 

It's fairly common, I have seen the same post about 2nd gen Rams in other boards - no real solution though....

 

Its defiantly not engine ping, and im quite sure its not a loose heat shield or anything like that, as it is RPM specific, and only happens when in motion. You can rev the crap out of it in the driveway stationary and it never happens.

Its gotta be drive train, front/rear end, or possibly something in the tranny. On my particular truck it sounds like its coming from the drivers side, front of the truck. I don't believe its a wheel bearing, as again, RPM specific, and its not the "clicking" sound you generally get with a bad bearing.

 

Get four jack stands, and support the truck on the axles, run it like that a bit, see if you hear anyting. If ya don't, step on the brake, and do the same thing. (doing it in 4wd may not be such a bad plan either.....)

 

Now i see you have a new cat, but mine does the same, exact same thing and i have a stock cat( i think my internals are coming apart) because when i went looking for the rattle, i could only find it if i hit on the exhaust, and its not my muffler because i just replaced it, and my heat shield isnt loose or rattle on something, and thts just where the damn noise seems to be coming from, so im ording a new high flow magnaflow cat thats supposed to just bolt right onto the headers and fit with the existing pipes, hopefully it cures my rattle, and makes my truck a little louder

 

I think I have found the noise, I am 90% sure it's the torque converter. I had a brand new Chrysler Transmission installed back in 2009, since it was installed I have noticed the truck would slip when it was stone cold for the first 10 seconds then be fine. I also noticed had problems with what I thought was a misadjusted fickdown cable, could never get it adjusted right.

Here is the old post from a long time ago with this issue that I never fixed: https://dodgeforum.com/forum/1st-gen...ues-hydra.html

The truck would feel like it would buck on the highway under light throttle, almost like it wanted to kick down or so I thought. I did not have time to bring it back to the trans shop since I am now stationed in Fort Carson, CO.

I of course have this noise which sounds like it's from the driverside. With the windows up, the noise can be heard better. I have also noticed a rough shift between gears, almost like a loose transmission mount would feel. The transmission it's self is shifting correctly, fluid looks great, no slipping other then that first initial, when stone cold, start off.

I wonder if I am seeing the slow decline of this torque converter, which I am not sure if the trans shop changed....

 

I am going to take it to a local transmission shop to verify the TC issue. I may just do it myself in my garage although I have a 4x4 and will have to pull the trans and transfer case but at least I have a little more ground clearance.

I am guessing a trans shop would charge around $500 for the job, but I wonder if the pump should be changed since the trans will be out even though the trans is a new Chrysler trans installed in 2009?

Also, who can direct me to the a better then OEM TC that helps with low end torque (towing)?

The truck will eventually have the 408 Stoker when I get around to ordering the kit, machine shop ect.

 

Update: The noise got a little worse or easier to hear. Also shifting between gears has got harder. The truck will buck a bit between gears, trans mount is not broken. This noise has been there a LONG time.

I put the rear wheels on jack stands, had the wife simulate a driving condition. Could not hear a thing because there was no resistance. So I had her lightly apply the break at 30-40 MPH under light throttle. Bam, created the noise and it is coming from the front of the bellhousing on the transmission. I am going to pull the cover and have peak at the Torque Converter and flex plate.

This noise started as something that was hard to hear and got louder over time. Maybe it is a bad Torque Converter or maybe it's a bad pump... I want to see if there is any signs of wear or rubbing.

 

Drop the trans pan, and see if you find anything interesting in there.