Need help with diagnosing noise in serpentine belt system.

[sangretdi]

Engine has developed what I'd describe as a "metallic drone".
When I remove the serpentine belt the sounds goes away.
I haven't been able to pin-point which component it's coming from.
When I spin all the pulleys in the system I don't hear or feel any usual noises/grinding, etc

I replaced the tensioner/shock and alternator pulley when I did the timing belt couple years ago. Had a shop rebuild the alternator at the same time.

The A/C compressor was replaced by the previous owner with some non-OEM deal. The AC hasn't worked in months, 99% sure it's just the clutch coil that has died. Just haven't had the time to deal with it. spins fine.

So the only original components are the power steering pump and the serpentine "roller".

Power steering pump is topped off, doesn't make any odd noises when turning the wheel. Loses no fluid. When I spin the pulley it sounds fine/no grinding, but it doesn't spin very long... maybe 1.5-2x around. compared to the other components which I'd guess spin 4-5X around. My gut says it should be the culprit, but with my ear near it, I don't hear the noise really any louder... and I hate to just throw money/new parts at the problem hoping it'll do it...

Any good advice/tricks to track down the culprit?

 

[Tdijarhead]

Shut the engine off spray some wd40 into the back of what you think is the offending pulley. Start the car back up. Do you still have the sound, has it changed in tone? If it's still there repeat on the rest of the pulleys until you find the culprit.

 

[UhOh]

Pretty much sounds like you know what's causing the noise. I wonder whether you could, with the belt off, wrap a bunch of string around that pulley and then yank the string to try and get that roller to spin quickly.

 

[turbovan+tdi]

Does the alternator pulley rotate backwards?

Is the tensioner really jumping around? I've had one that looked new go bad. Push on it to load up the belt more, WATCH your fingers, does the noise go away? Is it leaking?

 

[Metal Man]

Most problems with the serpentine belt system are caused by a bad (frozen) alternator pulley. Noise, it's the pulley. Belt tensioner jumps around, it's the pulley. The new tensioner you just put on because it was jumping around is now broken, it's the pulley.

 

[sangretdi]

Shut the engine off spray some wd40 into the back of what you think is the offending pulley. Start the car back up. Do you still have the sound, has it changed in tone? If it's still there repeat on the rest of the pulleys until you find the culprit.

makes sense and i gave it a shot. removed the pulley off of the p.s. pump, but the flange it mounts to blocks the spray from hitting the bearing, that i assume is behind it. I'll give it another go tomorrow, maybe tilt the pump itself face up and let gravity get the wd-40 in there.

 

[sangretdi]

Pretty much sounds like you know what's causing the noise. I wonder whether you could, with the belt off, wrap a bunch of string around that pulley and then yank the string to try and get that roller to spin quickly.

i think this is a good idea. i'd like to find a shorter belt and maybe use my drill to spool it up...

 

[sangretdi]

Does the alternator pulley rotate backwards?

Is the tensioner really jumping around? I've had one that looked new go bad. Push on it to load up the belt more, WATCH your fingers, does the noise go away? Is it leaking?

i just double checked, stuck a chop stick in the alternator and it only spins one direction, as it should. i did put a quality pulley on the alternator not too long ago. same with the tensioner, fairly new, and no jumping

 

[sangretdi]

Most problems with the serpentine belt system are caused by a bad (frozen) alternator pulley. Noise, it's the pulley. Belt tensioner jumps around, it's the pulley. The new tensioner you just put on because it was jumping around is now broken, it's the pulley.

yup, as preventative maintenance replaced both when i did the timing belt. they seem to be holding up.

 

[sangretdi]

maybe the p.s. pump and pulley is working as it should? there is more resistance when it turns compared to the rest of the pulleys, but it does have fluid sloshing around in there an driving a pump, yes?

going to pick-up a cheap mechanics stethescope also...

 

[Metal Man]

Yes, a stethoscope is very handy. It sounds like the only thing you haven't changed is the power steering pump.

 

[sangretdi]

I haven't been active on the site in a while, looping back around in case anyone else is searching the archives with the same issue:

Turned out to be the alternator- It had been rebuilt by a local alternator shop, had less than 10K miles on it before the bearing puked. After reading about the importance of German bearings on here, I asked the guy if they were German. He said "he wasn't sure, no one had ever asked him that before and it makes no difference" but wouldl replace the bearing for free under warrantee. I opted not to and bought one from IDparts. 10K+ miles so far on that one with no problems.