For a while now, I've been hearing a loud whining noise upon initial acceleration. It sounds like a supercharger. It hasn't been getting any worse, but its still a nuisance simply because I know it wasn't there before. I first suspected the alternator, but I recently tested the voltage and it seems to be working fine. Transmission issue? Any ideas?

 

Hi XJ8JR,

Do you hear the sound while revving the engine with the car in Park, or only when in gear and actually moving?

Don

 

If it was, for example, the alternator, then worn, whining bearings would not prevent it generating electricity.

Good question above, the other is, does the pitch go up and down with road speed or with engine speed.

 

I have the same noise.
I have researched it and found that:

A. I had the noise before and after a transmission oil/filter change recently.
B. Sometimes the noise is absent when the AC is off.
C. I will be changing the serpentine belt and pulleys shortly to see if its those.
D. I have a leak in the Rear Differential Gearbox that might have been it. However this was refilled with oil ( leak not fixed) and the noise still continues.

I was almost certain it was the transmission.
I was then almost certain it was the shaft and rear diff.
Now I am working on the serp belt and pulleys.

I will keep you informed.

 

I just tried revving while in Park, and the whining was still there, but not as loud as when in gear and moving.

The pitch seems to go up with engine speed, but its only noticeable upon initial acceleration. I think the road and engine noise end up drowning it out. You can also hear it very slightly while coasting at high speed; the pitch going down along with the speed.

A. I also have recently had a transmission fluid change. No change.
B. The noise is still present when A/C is on.
C. I recently changed my serpentine belt, idler pulley and tensioner. No change.
D. I had thought about the rear diff, but haven't yet taken the time to inspect it.

There were other symptoms that lead me to believe it was the alternator: RPMs sometimes drop to 500 a few seconds after coming to a stop, the A/C is running rough and accentuates the RPM drop while braking along with an odd almost grinding noise, and RPMs drop when turning the steering wheel at low speeds. All this lead me to believe that perhaps the extra load wasn't being handled properly by the possibly failing alternator. But when I tested the voltage, everything seemed ok.

 

The A/C compressor can cause a whine when the gas is low. I was convinced the transmission was on the way out on my 04 X350 but eventually realised that the noise didn't happen when the A/C was switched off.

Once the A/C was evacuated then filled with the correct amount of gas the noise went away.

You can test by switching the A/C off and see if the noise goes away.

 

The noise is present whether the A/C is on or off.

 

I am experiencing a similar whining noise but appears to be coming from the rear passenger side. Noise goes away when I take my foot off of the accelerator but returns when I re-apply pressure to the accelerator. I have recently changed the transmission pan filter and replaced with synthetic ZF fluid. The noise is still there. I have tried to drain the rear diff. but cannot get a pipe into the fill plug hole as it does not have a drain plug in the diff. I was thinking of dropping the differential and servicing it. Any suggestions.

 

You should be able to get a rubber tube through the full plug access hole in the diff. Purchase a transfer pump from Harbor Freight which will make the process easier. Any shiny diff oil or metal shavings on the fill plug (which has a magnet on the end) could mean trouble...

 

to help find source of noise in the engine compartment you can put a pipe or rod and place it carefully in direct contact with the alternator and also the supercharger. Then place the other end to your ear. If there is a bad bearing or other wear you will detect a difference. Appears to be rather crude technique but id does work

RyeJag

 

or the posh version, an "Engineer's Stethoscope" which might be a few pounds on fleabay.