I have a suspicion that it's likely a form of spark knock/pinging, but it doesn't hurt to tap the knowledge here.

Truck is a 1998 Dakota Sport, 3.9L Magnum. There's a light rattle, which kinda reminded me of dry needle bearings of a bad u-joint, although not as loud/constant. My experience with that noise was halfway to work in a 1978 Chevy pickup and it was almost like metallic popcorn, whoops, parkinglot fix anyone? Example is this video (not mine) between 40 and 55 seconds:
Just what it reminded me of the first time I heard it, just muffled.

ANYWAY, it's obviously not that, as it's nowhere near constant, and actually quite random to actually happen. I wanted to post this awhile back, I just never got a good recording with how random (and quiet) it was. I'm lead to believe it's pinging as it happens when the engine has a chance to get on the warmer side. i.e. idling in traffic, slow town driving, ambient temps 85+, or if I shut it off ~15 minutes (letting the block heat soak with no flowing coolant) and restarting and going somewhere. It's not constant by any means, for the most part it's 1500-1900RPMs and might do it just cruising through town, but again, only random. Outside of that RPM range, pretty much nothing.

The easiest way to get it to make the sound is "blip" the gas when the TC is locked up, but not enough to unlock it. However, it only rattles a couple times. If I hard accelerate or cruise at over 2k RPMs (i.e. highway/interstate), it will not make a peep. This is the confusing part for me, I figured a ping would keep making a racket during hard acceleration. It also keeps quiet if I'm cruising 55+ generally, I guess the wind is enough to keep it just cool enough. It's most annoying in traffic, stop and go, since I have to feather the gas.

It's not really loud and it was hard enough to get someone else to hear it. The only other person to kinda hear it said it sounded like lifter rattle. My only thought of how it would be lifter rattle is if the hotter oil thinned just enough to not pump the lifter, but when I hit it, oil pressure pumps it up. Although, I never have an issue with oil pressure, for the most part it stays above the midway line. Along the lines of pinging: I haven't really seen any improvement trying midgrade, and I can't really afford to try further tests with it with how random it is. Gas jumped another $0.14 today... I knew I should have got gas on the way to work and not after... Quality of gas is a non-issue as well. I've tried from multiple stations (70% of the time I run Exxon or Shell, this time was a rare Citgo, no changes) The first time I noticed it, I was running Autolite 3923 coppers as well, so they're out as a 'solution' Doesn't really use too much oil. I used maybe a quart on a 2154 mile round trip to Canada doing 75mph all the way, figured that's about right for blow-by and a light leak at the back of the engine. Figured if it was a plenum, I'd be eating a lot more oil than that, also the pan was dry last time I had the TB off.

Mostly seems to be a slight annoyance to me, I can never have a vehicle without SOMETHING making a sound... The following is about the best recording I finally managed and it's only in the last 4 seconds of the video.


Let me know what you think.