unusual squeal/ringing under accel

[highly]

OK, having a very unusual sound in a MK4 Golf TDi ALH. It only happens under moderate (normal) acceleration and only in 1st or second gear. It starts at 2800 and continues to 3800 RPM. It sounds somewhat like a brake squeal in nature, but more like when you make a crystal wine glass 'ring' by rubbing the rim much like a pulley ringing.

I've checked things out with VagCom and found nothing. I've lifted the car up and put it in gear accelerating through the RPM range and nothing. Pulled the wheels and checked all associated moving parts for unusual wear. It never happens in any other gears or at any other RPM ranges. Brakes are good, no obvious play in the front wheel bearings. Axles/boots are all good. I visually inspected all drivetrain parts and see no rubbing or indication of chafing anywhere. No apparent soot from EGR pipes. Some oil in the boost pipes, but just a coating.

The sound comes from the front of the car and seems like it's from the driver side. Recent changes to the car in the last 10k miles are a new 100k timing belt, all timing pulleys, water pump, serpentine belt, and the car was chipped w/ new nozzles. Timing belt and path looks clean and VCDS tdi fuel timing checker is just a little advanced. Checked the EGR system and there are no sooty leaks indicating a problem there.

Troubleshooting today, I found the VNT actuator sticking. Removed, cleaned, verified, and replaced. Pulled the serp belt and verified correct function of the clutched alternator pulley. Operates properly, but replaced anyway because I don't know how old it is. New one was stiffer in freewheel direction. Did vacuum testing and found that the small line from the vac pump at the valve/tee does not hold vacuum (removed small line from the tee, applied mityvac to line). Troubleshooting indicates that the N75 valve allows air to pass when mityvac is on the top nipple, car turned off. Everything else on the circuit holds vac. This doesn't seem right. Should it do that?

I'm stumped on the noise. Took a 12' piece of silicone tubing and stuck it in the engine bay near numerous items with the other end stuck in my ear while driving to find the ring. No luck so far. Tried transmission, vac pump, Brake booster, N75 valve, and power steering pulley. Nothing. I'll continue when the wife is done using the car later today.

Anyone with ideas?

[chittychittybangbang]

I haven't taken it apart but your N75 sounds like it's working.

No clue on noise. It could be some load is causing noise in the transmission or turbo. You already ruled out brake, alt pulley, and belt noise.

[Seatman]

Is it possible to get a recording of the noise at all?

[Fluid]

I'd say it was an intake resonance but that's not a complaint unless you modified the intake. You already checked the EGR pipes for soot deposits but also check the intake hoses for leaks. Do you have a rust hole in the exhaust that's whistling?

Maybe you have a bad pulley on the timing belt? You said the timing belt was changed in the last 10k, maybe you have a defective part. Where did you get the parts?

It's not the chip or nozzles.

[bbogdanmircea]

Hello.
I have a similar problem and still couldn't find a fix for it.
The sound that I hear is like a ringing or vibration.
I thought it was from the alternator pulley so I changed and and the alternator spring tensioner too.
What I observed is that after I changed the spring tensioner the sound seems to apper in a broader rpm range. So I deducted that it some component on the accesories belt that has a problem.
I hear this sound in any gear, when the engine is from 2000 to about 2500 rpm so at maximum engine torque.
It's more like a vibration.
I suspect the alternator rollers maybe or the powersteering pump rollers...
I'm not sure at all, many mechanics said different things, already invested in the alternator pulley and tensioner for nothing...
I will try to remove the accesories belt and run the car whitout it to see for sure if the noise is from the accesories belt. If it still appers then it may be from the timing belt or something else.

[almir]

if you still have TB cover removed then check your TB idler pulley. Many people complain about their idler pulley bolt breaking for some reason. Maybe your is giving you some signs.

[k4u2luz2]

I have the exact same problem in my 2006 and it is killing me. I have checked all the things you have all mentioned and still can't diagnose. The only thing I can think of is, it must be the bearing on the impeller shaft of the turbo. Anyone...open for more ideas.

Keith

[highly]

Originally Posted by k4u2luz2

I have the exact same problem in my 2006 and it is killing me. I have checked all the things you have all mentioned and still can't diagnose. The only thing I can think of is, it must be the bearing on the impeller shaft of the turbo. Anyone...open for more ideas.

Keith

My case turned out to be an exhaust leak (of all things!). The corrugated hard pipe on the EGR was cracked. When the pipe finally split the squeal became a more recognizable sound and I was able to locate it. Even if it seems intact, pull it off and check it. Bet it comes out in more than one piece!

Hope that helps!
-Todd

[mountain lion]

Hi - I have this exact same sound under the same conditions on my 2004 PD (110k miles). Before this loud squeal, a feint ticking developed that sounds like a rock in the tire tread or metal tapping, but I can only hear it under load / moderate throttle. My first thought was exhaust leak somewhere based on when it would happen, but I had no way to locate it. The tick is still actually there, but now I have the squeal to go along with it.

Assuming I have the same issue, would EGR block off plates effectively stop the noises and the leak? I have a tune so CEL's will not be an issue. I'd prefer to leave everything stock, but don't want to buy a whole new egr setup if the block off is easier. Thanks

[highly]

Originally Posted by mountain lion

Hi - I have this exact same sound under the same conditions on my 2004 PD (110k miles). Before this loud squeal, a feint ticking developed that sounds like a rock in the tire tread or metal tapping, but I can only hear it under load / moderate throttle. My first thought was exhaust leak somewhere based on when it would happen, but I had no way to locate it. The tick is still actually there, but now I have the squeal to go along with it.

Assuming I have the same issue, would EGR block off plates effectively stop the noises and the leak? I have a tune so CEL's will not be an issue. I'd prefer to leave everything stock, but don't want to buy a whole new egr setup if the block off is easier. Thanks

I'd say that if the EGR blockoff doesn't fix it then you've effectively diagnosed that the hardline isn't the problem. Alternately you could remove the hardline and when it falls apart in your hand you will know that was the culprit and it's time to buy blockoff plates.