Metallic, ringing sound

OK, I need some help from wiser minds than mine.

The patient: 2003 ALH 5 spd 190k miles

The symptoms: I have been trying to track down an irregular, non-rhythmic metallic ringing sound that reminds me of a metal plate rattling against something else, like a pulley, bolt or large washer would. It is easiest to hear over typical diesel clatter between 2000 and 3000 rpm. I believe it happens at other rpms as well, but it's often covered over by typical engine noise.

The treatment, so far:

1. Ruled out rocks behind the ABS ring, the noise can sometimes happen if you rev the motor at rest. I did learn that it's easier to hear with hood down rather than opened. Open the hood and it gets drowned out.

2. Removed serp. belt to no avail, so alternator pulley, ps pulley, etc. are ruled out.

3. Inspected and removed EGR cooler. No leaks, installed block-off plates that were sitting in the garage, the noise continues. Exhaust manifold, downpipe and exhaust are tight and solid.

4. Spent lots of quality time looking for anything loose under the hood. Everything seems tight and secure.

5. Spent lots of quality time listening with a stethoscope for unusual sounds. Cam, lifters, injectors, and injection pump sound normal.

6. Sway bar brackets, ball joints, tie rods are all tight, etc. Struts, springs, strut mounts are good too.

7. Removed upper timing belt cover. Upper roller is clean and moves smoothly.


Not sure where to go at this point.... Brake rotors? Harmonic balancer?

Any ideas are appreciated....it's driving me nuts.

Thanks!

i usually don’t comment on these because i have a feeling i’m always way off. but no one else has yet, so i’m gonna ask about the wheel bearings... could it be something failing or something related to that? or maybe something breaking apart in the transmission/clutch/flywheel?

I feel like those things would have a rhythmic pattern to the noise, but perhaps. idk. i’m no mechanic. lol

sorry.

where do you hear it coming from? Could it be an exhaust component/hanger?

Check your heat shields under your car. The "speed nuts" often rust away and the shields then droop down and vibrate against things. Might be exhaust related (note that heat shields and the exhaust systems are pretty closely paired). Note, however, that sounds related to these components tend to be more clang-y and with a higher pitch sound.

That would be my suggestion as well.

If it does it in neutral while reving - that should rule out brakes/bearings, etc. Try it in neutral - clutch in vs out to see if the noise changes - that could point to a bad DMF.

I third the speed nuts holding the heatshield in place, mine rusted completely off and made an awful sounding metallic racket. I picked up a few from the local dealership that didn't look the same, but functioned well
(not my pic and not the replacement washer either, but the rusted piece is what it looks like... there are 6 or 8 throughout)

Does your car use a dual mass flywheel?
I had one on my Ford diesel and when it when out I got a sound like a rocks in a can with a bit of ringing metal. I could not track it down, thought the guts of the muffler were loose, changed that, NOPE.
Finally had to change the engine and put in a solid flywheel when I did, noise all gone.

Thanks for all the good ideas. Luckily, it doesn't seem to be DMF --the noise is consistent whether or not the clutch is in or out.

This weekend, I'm going to crawl underneath and check the heat shields. That completely escaped my thought process.

Thanks again for all the great input.

It could also be the 2nd exhaust mount is rusted off. It makes this jingle/metal ringing when it comes loose.