Droning noise at 60 mph
 

Hi, I've noticed a quiet droning noise as the speed decays through 60 mph on a trailing throttle. Been happening for several months without really changing. It happens in 5th or 6th gear and is immediately abolished by shifting into neutral. Gears shift well and car also drives well with no noises when cruising at 85 - just returned from the Alps. It is not tyres as still happening when I fitted the spares with snow tyres. I recently had the gearbox oil level checked and topped up and there's nothing on VAGCOM. Car is a 3 litre diesel sport with 94k miles and FSH. I recently replaced the front C links which improved the handling but made no difference. Any suggestions?
Cheers,
Jem.

I've seen transmission drone on a D3 before, quite noticable wheel speed not engine speed and it went after a gearbox oil change.

I did also have a wheel bearing which manifested itself as a rumble only in certain situations. That was at around that mileage.

That got progressively worse though over a few hundred miles, which you'd easily notice if you're doing some miles in it, so maybe thats less likely.

Try changing all the transmission fluids with OE fluid.

Autobox is easy for a garage, maybe a little difficult for DIY because you need the car in the air and level

Rear diff (easy as there is a drain plug and fill plug)

Front diff (you need a vacuum pump such as a Pela) and then it's quite easy.

The torsen transfer case looks difficult to get oil in and out due to being up in the tunnel and the adjacent exhaust pipes and I have never found a how-to.

interesting ... i see many videos of people shifting into neutral while doing about 50 mph and then putting it back into drive ... is this safe to do on an auto box ? ive never done it.

Done it accidentally before... but I'd guess that the software would have a routine for that.

I tried shifting into neutral to get a feel for where the noise might be coming from, not something I usually do but hasn't upset the car as far as I can tell. The gears still shift almost imperceptibly and above 60 mph the car is absolutely normal. The noise does not occur in neutral but is the same whether in 5th or 6th gear. It's not very loud and wouldn't easily be noticed with the radio on. I'm not a mechanic but this suggests it involves the output end of the gearbox before the torque converter? Is there an intermediate bearing? I'm probably over analysing and its a case of ATF change and see. I was interested if anyone noticed a similar issue. Thanks for suggestions.
Jem

If you shift accidentally into neutral most car manuals tell you to allow the engine to drop to idle and then put the car back into D - should be no different to the car coasting already in D so won't do any damage.

Thats ok then so if im doing 50mph and put it in N i can still coast but let the revs drop befor putting it back in gear ?

Well I took the jump and and had the ATF fluid changed last week with ZF Lifeguard 8 as it was quite a lot less expensive than Audi OEM and highly rated by those in the know apparently. The old fluid didn't look too bad and there wasn't much stuck to the sump magnets at the time of draining (mileage exactly 100K). Since then I took a highly entertaining run to Ayrshire at the weekend to give it a good shakedown including fairly rapid run back down the A71. The verdict? The gearchange which was very smooth before is now all but imperceptible and seems faster in tiptronic mode. The car seems to drive even more effortlessly and there is also a marginal improvement in the recorded average mpg from 36.7 to 37.5. I wasn't expecting this but the car returned an indicated 41.6mpg for the Scotland journey and I wasn't hanging around which even impressed my diesel hatchback owning passenger. The droning noise however is still there and doesn't really seem to have changed. This was disappointing but the improved driving characteristics and confidence from having renewed the oil certainly justify the expense for me.