Have been lurking and not done many posts, but I need some help now. Here goes:

I am at a loss regarding a whirring noise coming from the passenger foot well of my w202 C240T.
Driving slowly forward, I hear a distinct whirring which disappears with some speed as it gets drowned out by other mechanical and road noise. It is not an engine noise because at idle and when stopped, the whirring is not there.
Here is what I have done up till now.
1. Checked closely under the vehicle to see if anything was hanging or untied: Nothing
2. Changed front wheel bearings. No change
3. Cleaned and checked wheel hubs: Nothing
4. Changed front and rear brake rotors: No change
5. Checked closely brake callipers: Nothing
6. Changed front and rear brake pads: No change
7. Flushed and bled the brakes: No change apart from a nice firm pedal now
8. Checked steering box holding bolts and controlled torque level: Nothing
9. ATF and filter have been changed recently during last service
10. Rear diff oil changed also during last service
11. Transmission shaft and central bearing checked

After all the above work, I took the car to my trusty mechanic to he could check what I had done and get his ideas on the reason for the noise. He checked everything again and didn’t find anything. His only comment was that the noise could be in the tranny and I shouldn’t be worried. Well I am as the vehicle is my trusty steed, especially in winter as my other car a C43 will be stored away and kept off the cold and salty roads.
So, does anybody have any idea what is wrong, what could be checked over and the cause for the whirring? Greatly appreciate any ideas and comments. Thanks

Shifter bushings?

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

No, don't think so as no sloppyness or play in the assembly

What year? It's not a W203?

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

No, it's a W202 1998 C240 V6 Estate

So it doesn't change with speed, it's present at idle or only while driving? What about just revving the motor, any change?

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

A 2.4 V6? Sorry, I just never heard of it.

Tire noise?

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

2.4 V6 is the M112 engine, which was standard in all European versions of the 2.4. Perhaps it wasn't imported in the USA...

Rear bearings?

Perhaps you can get your car on a dynamometer and have someone listen for the whirring noise from outside the car to pinpoint the source.

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Fred Hoelzle

No noise at idle. The whirring only appears when moving forward and increases with speed until it gets lost with other mechanical noises.

Something in the driveline for sure. Diff, driveshaft, has to be in there somewhere. Well, doesnt HAVE to be, but with all the other stuff you've checked and done.......hm

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL