I have a 2001 Ram with a 318. It has 85K miles. Recently it started making a noise that sounds similar to engine pinging. However, it is more metallic sounding, and does not change with engine load or RPM. It goes away at idle. Once the truck sits, you have to drive it about 8 miles before the noise starts. It seems to get a bit louder the more you drive. Putting a load on the serpentine belt seems to make it louder, like turning on the air conditioner. The alternator and idler pully were changed to no avail. I've pulled the belt off and had a good look at the various things, water pump, idler, compressor and none seem to have bearing issues. The noise is most noticeable around 1300 to 1500 RPM. You can hear it best around 35 MPH, since the road noise is quieter at that speed, however, it is very noticeable at 55 once you drive it a few miles too. Sometimes it is louder and sometimes not so much, but still there. I'm stumped. The frequency of the nose does not change with RPM. Anyone had similar problems? This is driving me nuts.

I attached a MP3 audio clip, but it is very short in duration, because of the file limit size you can upload. You have to list carefully to hear it. It is a hard thing to record over the road noise from inside the cab.

 

Can't make out the noise in the clip but take off the serpentine belt and run the motor. See if the sound goes away. Might be the tensioner.

 

Thanks for the reply. We were just about to do that, we had the belt off at one point to check the various bearings by hand. We noticed the noise would stop if the airconditioner compressor was shut off. So we thought it was the compressor.

Then I let the truck cool off and took it for a long drive in the evening with the air off. It took a while but the noise came back. Turning on the air seemed to make it louder, but I don't think it is the compressor. I think the added load on the belt is just making whatever is the problem louder. The noise in the clip is hard to hear, but it is a rapid tink, tink, tink. It does not change in frequency with load or RPM, but goes away at idle.

I'm pretty sure if I remove the belt, it will go away. The idler was changed and also the alternator. Maybe the water pump? I don't know.

 

I was able to isolate the noise from the road noise and attached a better sound clip.

 

Still hard to make out. Does it happen only in drive or can you rev the motor in neutral and hear it?

 

You can hear it in neutral if you rev the engine a bit, like 1300 to 1500 RPM.