Darn. Time to reset the "X Days Without a Needed Repair" sign in my garage.

Big green kitty (03 S-Type, V6 base model) has developed a new noise. I'm planning to be under the hood and on my back this weekend anyway flushing coolant, so advice on isolating the noise's culprit would be greatly appreciated:


Noise occurs on city streets above 20mph, but so far only after the car has been on a highway driving above 50mph. When getting on and off the highway, no noise. But within a block of coming off an off ramp, the noise appears, then goes away two, three, or four traffic lights later. Noise is present accellerating, deccellerating, coasting, while braking with "sport" mode on or off, and even in neutral. Sound volume and pitch do not change with speed, but go away immediately when the vehicle drops to less than 20mph.

No warning lights on dash, no codes I can read with an ELM scanner and torque app, no affect on engine rpms, shifting, or vehicle power. Tires have good tread and are all properly inflated.

Thoughts:
a. Bearing? (no shaking and doesn't change with turning wheels, so not thinking wheel bearing...)
b. rear differential? (not seen any leaks in garage)
c. Torque Converter - but if so, wouldn't I see problems shifting or lack of power? Especially driving around between 40-50mph.
d. Exhaust leak
e. Gremlins

 

I have had several wheel bearings fail that had similar symptoms, noise and no shaking or change in pitch with turning. Does the noise increase with speed? Can you isolate the noise to one corner of the car?

 

Hi,
I have a similar thing on my '06 2.7D S Type. I'm pretty sure it's coming from the diff as it seems to be rear centre in origine. No leeks are apparent but I'm thinking of having the diff oil changed and check for movement/play at the same time. Can anyone help please?
John