This Noise

[RBBailey]

The Tdi is noticeably smoother and quieter after a recent valve adjustment, and after advancing the timing.

However, now I'm finally able to really hear the ringing noise I've been trying to track down for some time. To preface -- when I hear valves clack, they "clack". When the knock on the 2.25 in the Series was hardly pin drop, I knew what I was hearing right away. And as it developed, it had the sound of "knocking" on hardwood. When the V8 used to clack because of low quality, or low octane fuel, that's exactly what it sounded like; it had a "thin clack".

What I'm hearing is a distinct, repetitive ring.

Now that the engine is running so smoothly, and therefore quieter, I was able to catch it on video. I'm sure you'll hear it, but in the video is sounds a bit more like just a tap-tap-tap. In real life, that tap is a metallic ring.

https://flic.kr/p/GC1EFt

It is pretty clearly coming from the front of the engine. In fact, I used to only be able to hear it by bending down in front of the radiator. But I can't seem to be able to pin-point it with a stethoscope, except for at the thermostat housing!

 

[rocky]

Be interesting to remove the serpentine belt and see if any of the pulleys or tensioner have excessive or erratic movement...

 

[RBBailey]

I have thought of that.

 

[RBBailey]

I just got back from a track meet that was much quicker than usual, so I'm going to see what I find.



The reason I also thought of doing this is because the sound is almost exactly like what it sounds like when you knock into the idler pulley, or the crank pulley. None of them "look" strange when spinning from the outside, so...


Other than some obvious thing, what do you think I should do to inspect for a problem?

 

[RBBailey]

No indication that there is anything wrong with any of the pulleys.

 

[RBBailey]

Also, I have to admit that I ran the truck for a minute without the belt in place to see if the noise was still there -- it was.

 

[Jeff B]

Hard to tell over the innerweb, but I think your motor sounds pretty good!


.

 

[rocky]

I. give.up. Button it back up, stop worrying and drive.

 

[RDavisinVA]

Rocky nailed it in post #2.
Idler pulley squeak.

 

[RBBailey]

I hope you're right. The pulley spins freely, and without wobble or noise. And the sound is there when the serpentine belt is not on.

Stick your head in a large cast iron pot, have a friend knock on that pot with a rubber mallet, that's what I hear. It gets lost in recording because of all other engine noise, but if I'm in the garage while the engine is running, if that noise is happening, my ears start ringing the same as if I just fired a gun without hearing protection.

 

[RBBailey]

I took the truck to Ship’s this afternoon. The ringing bell was loud enough that the guy at the gas station asked about it. But when I got to the shop the noise went away...

Not to worry though. It came back on the way home. ...Rovers

What if I just assume this is a funny sounding knock? What would be my steps at this point?

 

[RDavisinVA]

Get a stethoscope and find the source of the noise.

 

[RBBailey]

Been trying.

The only place where I think I hear something that is following the same beat, at least, is in the thermostat area. But the noise itself seems to come from about halfway down the front of the engine. I get nothing off the front cover, and any other noise I hear is a different rhythm.

 

[Contractor]

So this one time I had a loose bolt that would slide forward out of its hole sometimes and ring like a bell when it hit the fan. Then it would go back into its hole and stop.

Have you checked anything like that.

 

[RBBailey]

I've actually thought of that! Because that is a lot like what I imagine it would sound like. I've done some checking, but the only obvious bolts are all secure. Now that I know someone else had something like that, I might need to check more carefully.

I'm not running a fan, so it wouldn't be the same bolt, but it's a thought.

 

[rocky]

Leave it with Skip for a few days. Tell him to drive it daily.

 

[RBBailey]

Don't know him. But I was thinking of the same thing. Was trying to think who I could give it to that knows the 300.

 

[rocky]

I meant Ship....dam you auto corrupt....

 

[RBBailey]

Yeah, he literally has no place to park another vehicle right now.

Finally! I think I really did capture the noise. I picked up an auxiliary microphone and used it with my real camera. It was sitting there at 190 degrees after a highway drive, then coming up the hill. You can hear the ping/bing/ring/knock over the top of the rest of the noise from the engine. The first 20 seconds or so are mixed, but by the time you watch the whole thing, I'm pretty sure you'll hear it. I'm listening to it on an old laptop, and I can see the noise on the sound/amplitude graph on the computer screen.

https://flic.kr/p/GKyTw2

 

[MountainD]

What I hear, at least think I hear, is belt chirp. Maybe I am hearing something else, but I have had that chirp and thought it was more of a ring, but it was belt chirp. I could be totally off because I barely hear it, but take a spray bottle of some water and spray on the belt while it is running and see what transpires... It is also the sort of noise that can go totally away for a while... Usually just a slightly misaligned pulley, one too far in or out...