Hi Guys,

I have a 01 996 with 80,000 mile on it.

I have this squealing noise that comes on at low speed, stops at about 1800 rpm. Driving around parking lots brings out the sound. On start-up there is no sound, and usually take a few minutes of driving for the sound to appear.It sounds like it is the right rear

I have replaced the serpentine belt and spun the idler wheels. The power steering and the AC had a little bit of play in it, not much, but no sound when I spin them.

The steering is fine when driving.

The AC blows cold. And the sound comes on regardless if it is on or off.

I think the sound is coming from the AC unit. But it is really hard to nail down where it is coming from.

The sound is really annoying.

Anyone have any insights to this annoyance.

Thanks.

 

wheel bearing?

 

Is the noise present with the car stationary? If so then probably a problem with the accessory drive system.

Idler/tensioner rollers can make that noise, but not always.

I have had two idler/tensioner roller problems with my 2003 Turbo. First time there was a noise that sounded like a dry bearing. 2nd time there was a high pitched intermittent squeak, a chirp if you will. I had the tech replace all idlers and the tensioner as it was hard to know for sure which one was bad and I didn't want to go to the expense of replacing one at a time over time.

A water pump can also account for the noise.

With the belt removed -- carefully note its routing and direction of travel so you can install it the same way again -- give each accessory drive a test for excessive bearing play, both radial and axial play.

In my experience with a bad (and noisy) water pump the play wasn't much but it was more than the other accessory drives exhibited.

Also, one edge of the rather new belt was sharp. Because of the bearing play the belt wasn't tracking right and rubbing and this caused one edge to become sharp. If a belt has a sharp edge then almost certainly an accessory drive is bad.

If the noise is not present when the car is stationary then it is probably a dragging brake pad.

Wheel bearings don't usually emit a high pitched squeal. They groan or growl or emit a low pitched rumble and usually it takes some speed to make the bad one emit any noise at all.

One thing I have found over the years, with both my Porsches, is the brake hardware can get very dusty. The Boxster front wheels get almost black with brake dust which means all the brake hardware is just coated with this stuff.

The result is at very low speed the brakes emit a high pitched squeal that goes away when the brakes are used but returns after the pedal is released.

What I have found "cures" this -- for a while at any rate -- is to wash the brake hardware. I do this at the DIY car wash. I select the normal rinse setting and rinse each wheel and its brake hardware, the caliper and rotor.

I do not jam the wash nozzle that close to the brake caliper but I direct the spray at the caliper. The water runs black as it flushes the dust away from the brake hardware, the hub, and the wheel.

After i have done all 4 wheels then I switch to the spotless rinse setting which has a lower water pressure and get the nozzle closer to the calipers and other brake hardware to thoroughly rinse the dust away. What I'm particularly aiming at is the brake piston dust boots.

The heavy accumulation of dust on these boots interferes with the slight seal hysteresis that causes the pistons to retract slightly when the pedal is released and pull the pads away from the rotor. It is the pads or pad remaining in slight contact with the rotor while the car is moving at a slow speed that causes the squeal. At higher speeds any runout/free play at the wheel or bearing will have the rotor wobble just a tiny bit and the pads get moved away from the rotor and ends the noise.

If you go the wash the brake hardware route be sure afterwards you drive the car and use the brakes hard enough to get them hot to thoroughly dry the brakes. Otherwise, when you park the car the brakes will rust up something fierce.

 

Macster, Thanks for the detailed response.

I did the washing of the brakes with no positive result.

An update....

I went on a long drive the other day, and toward the end of the drive the noise was present at idle.

When I parked the car at home I let it idle and tried to really locate the noise without burning my face off.

The sound seems to be coming from the wheel arch vicinity, rather than the drive belts.

Could it be vibration related? Engine mount? Suspension bushing? Clutch?

Hope this update can give someone better insights.

 

If you want next time under the same conditions and the noise present, put a jack under the engine -- with a thin piece of plywood to protect the engine oil sump -- and jack up the engine just a bit. You want to only jack up the engine put enough force on it to change the loading of the engine mounts.

If it fits you can use the scissors jack. You are not going to pick up the engine let alone lift the car in doing this.

If the noise changes then very likely it arises from vibration. Engine (or tranny) mounts have to be suspect, but so to do exhaust hangers, heat shields, etc.

If the noise doesn't change, don't jack up the engine any more.

If the car is equipped with a manual transmission does the noise change when pushing the clutch pedal down?

If a Tip does the noise change if you shift from Park to D, N or R?

Does the noise change if you adjust the A/C temp control? Turn off the A/C compressor (extinguish the snow flake)? Completely turn off the cabin ventilation by setting the cabin fan speed to off?

Barring something above shedding more light on the source of the noise, my WAG is you'll find the noise coming from an accessory drive -- water pump is the most likely source -- or from an idler/tensioner roller bearing.

In this case then with the noise present and from under the car and being *very very* careful (mindful of the hot exhaust but also the rapidly spinning accessory drive belt) you or a tech will be able to pinpoint the source of the noise.

 

Just a long shot , but I had a freaky problem one time out of all the Porsches I have repaired, I have only seen this particular cause/symptom one time. It came from an Indy who had incorrectly diagnosed it as a clutch t/o bearing noise, and they had replaced the clutch, pressure plate, and t/o bearing. Although the noise was coming from the bell housing area, It was the rear main seal (RMS)that was squealing, BUT the cause of the RMS squealing was the air oil separator (AOS)failing. The failing AOS was causing the crankcase vacuum to be applied excessively to the rear main seal, which if a little too dry and in the right temperature would squeal. The quick check would be to get the noise to happen at idle, then with engine running try and remove oil cap. If the noise goes away, and the cap is difficult to remove followed by excessive vacuum noise then the AOS is causing the RMS to squeal.