Dean_Fuller

I think its the wheel bearing. Mine did the same thing about a year ago.

FiveElements

^^ I agree ^^

Try pulling the rear wheels, use a screw driver and open the brake pads so they don't drag on the rotors, then spin the hub and see if you hear bearing noise. It should be smooth and quiet.

The other possible problem is the rear bearing on the torque tube. That would suck to replace. You have to pull the trani.

kevin2012

My mechanic said that the noise is from my transmission primary pump and a total rebuild of transmission is the only way to fix it. And costs many thousands of USD. What do you think?
Cheers.

FRporscheman

If that's what you're facing, I'd say try checking (and possibly replacing) the wheel bearings first, because those are a piece of cake in comparison. Can you do the work yourself?

mickster

My tranny whined before rebuild. Possible.

1) How are the gear changes? Rough, smooth
2) Is the ATF reservoir set to the right level?
3) Does this mechanic have a lot of Porsche 928 and/or Mercedes transmission experience?

G8RB8

How old is the tranny fluid?

dr bob

The primary pump spins at engine speed, so your noise would be engine RPM related, not road speed related as you state for your noise.

Rear wheel bearings get noisier (more volume) as speed goes up, but the pitch (frequency) of the rumble doesn't change that much over the speed range. Tire noise gets louder and pitch increases with road speed increases.

Road-speed noises are usually between the pinion gear in the differential out to the lugnuts.

Hope this helps!

kevin2012

Thanks for all the advice. It is very informative. The transmission gears change smoothly in all range. Trans fluid and filter are changed yearly. Noise is speed dependent, max at 50~60 km/h when accelerate

So I will seek for a second opinion from another mechanic. Maybe I just change the rear bearings and see if it can fix the noise. Will update the result here. Cheers.

mickster

You have a mechanic looking for money, not a solution. Definitely find another on the Island or mainland.

vze2jshn

As someone recently suggested in another rear wheel bearing thread-- with an open road ahead of you sway from lane to lane and see if it affects the humming sound/vibration.

UpFixenDerPorsche

This might be useful:

mickster

Just following up--what did you find?

kevin2012

I have been busy and didnt spend much time with the car. Situation unchange. I might wait until the noise gets worser to identify it. I am thinking either the wheel bearings or the cv joints. I will update the findings here later. Cheers.

Tom in Austin

I would try a different wheel/tire back there just to eliminate the obvious possibility first. I put on my spare (a space-saver 996 type, not the OEM inflatable) and immediately found that my noise in back was from tire wear.

RFJ

Any chance its the ring and pinion? not even sure how to spell it. On my challenger I had a set go and that is about how it sounded. I have no idea if these r&p's would sound the same.Best,Ray