Mystery Squeal

Sorting out a 99 Miata at the moment and I'm having trouble with a mysterious Squeal.

The sound typically starts under hard acceleration, but can happen under any amount of throttle. I have gone miles without it occurring and then it happens twice in a mile. It sounds like it is coming from somewhere in the rear end.

It seems to be directly related to speed and when I stop, it doesn't start up again until sometime later.

I have replaced:

Rear hubs and rear bearings

Driveshaft

Brake pads and rotors

Thanks in advance for any leads. 

i would back off the rear (parking) brake adjusters another half turn and see if that fixes it.  I get a similar sound from my 95 SM at the end of a race at Blackhawk Farms.  After coming to a complete stop, the noise goes away.  By increasing the amount I back off the adjusters, it seems to reduce the noise.

Apologies, I should have mentioned that I removed the rear brake adjusters as well as the entire parking brake assembly. I should also mention that the sound stays the same whether or not I am pressing on the brakes or not (ie, I believe it is somewhere in the driveline). 

What Tom said...or maybe...nah. Obviously something that rotates and then stops with the car

Some thing rubbing on the axle, driveshaft or  rotor now and then.

Some thing rubbing on the axle, driveshaft or  rotor now and then.

A good thought. Im hoping its that simple. Ill see if I can find a lift this week to throw it on and see if I can replicate it. I was originally going to bring it to this guy: http://mazdamiataspecialist.com/ but he is pretty busy. Any other shops near Pasadena, CA that specialize in Miatas?

Clutch in and out?

Speedo cable?

its electronic.

Try jacking up the rear of the car so the tires are off the ground put it in gear be sure its blocked so its safe and then see if you can id the sound in the drive train.

Any chance it sounds like it's coming from right behind the driver?  If not ignore this wild ass guess.  It sounds like once it starts to squeal, the pitch of the squeal does not increase with speed but comes and goes with throttle load?  Hard to tell for sure from video but could it be a noisy fuel pump?

Clutch in and out?

 

Clutch in and out?

No difference on which gear I am in or if the clutch is in or out.

 

its electronic.

 

Try jacking up the rear of the car so the tires are off the ground put it in gear be sure its blocked so its safe and then see if you can id the sound in the drive train.

Interesting! I may just put it up on 4 sturdy jack stands and run it for a bit tomorrow to see if I can replicate it.

 

Any chance it sounds like it's coming from right behind the driver?  If not ignore this wild ass guess.  It sounds like once it starts to squeal, the pitch of the squeal does not increase with speed but comes and goes with throttle load?  Hard to tell for sure from video but could it be a noisy fuel pump?

Sadly not throttle load. I actually shut off the car and put it in neutral and the noise continues.

Ill put it up on jack stands tomorrow night to see if I can replicate. Ill report back then. 

+1 on checking fuel pump or fuel pump gasket at the tank.  Sounds a bit like a tea pot trying to vent pressure more than a mechanical squeal.  Maybe remove the covers over the fuel pump and see if it sounds louder or helps locate the sound.  Also check your gas filler cap isn't leaking - or just replace with a new one.

its electronic.
 .

check the hockey puck looking damper on the front of the diff.  I have heard of the breaking loose and causing mystery noises.  

check the hockey puck looking damper on the front of the diff.  I have heard of the breaking loose and causing mystery noises.  

The damper keeps spinning if you come to a fast stop.  I can't tell from his video if that is happening or not. 

Sloppy/wobbling pinion corkscrewing in and out is a possibility ....

http://youtu.be/NwLyrCbakeA

Update:

Happens when in any forward gear and neutral. Sound does not change between gears

Gets to a certain pitch around 20mph and stays there at any higher speed.

Only starts under load at around 20mph or higher

Once it starts, you can cut the engine and it still occurs. 

Replaced fuel pump. Replaced prop shaft. Damper is on tight. Rear hubs / bearings replaced.

Next up: Diff oil seals? Diff pinion bearing?

That is a strange one. It does not sound like drive-train as it does not seam to fluctuate with the speed. If the sound is coming from the tank area i would keep looking there. I know you replaced the pump,  but can you check the fuel pressure? There is a regulator at the bottom of the pump assembly, not sure if that could be it.  

At the end of you video it stopped, but your car was moving, is it intermittent?

You got a bad chipmunk in there. 

Update:

Happens when in any forward gear and neutral. Sound does not change between gears

Gets to a certain pitch around 20mph and stays there at any higher speed.

Only starts under load at around 20mph or higher

Once it starts, you can cut the engine and it still occurs. 

 

Replaced fuel pump. Replaced prop shaft. Damper is on tight. Rear hubs / bearings replaced.

 

Next up: Diff oil seals? Diff pinion bearing?

 

Cutting the engine with the ignition key eliminates some potential issue items.

Get a friend using a stethoscope take the ride with you. An automotive type stethoscope is dirt cheap.