Polo BlueGT mystery gearbox whine

[cornpop_2020]

Hi folks - first post, be gentle - apologies in advance for any slips on posting rules. Will rectify ASAP if pointed out to me.

The car:

Polo BlueGT 1.4 TSI ACT
2016
40k miles
in apparently good order, excellent physical condition when purchased a little over a year ago (with about 36k on clock)

Not long after buying, I noticed a faint-ish whirring noise, most apparent in second gear, but faintly audible at times in 3rd and 4th too. Sounds a little helicopter blade-like, with a definite rhythmic stutter to it. It increases/decreases in pitch with RPM - and is most audible just after letting go of the accelerator and allowing the car to slow on its own (but can also be heard more faintly while actively accelerating).

Noise seems to disappear when clutch is depressed. Gearbox was quite loud and clunky when changing through lower gears too.

A different, faint rubbing/clicking noise can often also be heard when idling in neutral, and this very obviously disappears as soon as the clutch is depressed. No idea if this is related or not but might help join the dots for someone who knows whats what...

Brought it back to dealer who, after a few attempts, acknowledged the problem and offered to replace gearbox with another, not quite new refurbished one (with 9k miles on it so newer than the car's existing). I agreed.

Not long after getting it back I noticed the noise was still there, almost identical to before - granted it did sound very slightly different (louder, whinier, less helicopter-like) and was only audible in 2nd and 4th.

Took it straight back, they agreed again, and replaced it again, with another refurbished gearbox. This time, the noise is at its quietest, and occasionally inaudible, but still there. Seems to go away when clutch is depressed, but there may be a very faint continued whirring (hard to tell - feel like I am going insane at this point).

I had it in a different garage (for separate unrelated work) once with the first box, and again when the second was in. The guy wasn't specifically looking at/for that noise, but he did mention it and said it was almost certainly gearbox related based on the fact that it SEEMS to go away with clutch depression.


My question is - based on how seemingly unlikely it is that 3 gearboxes in a row all had the same/very similar defects, and ruling out the dealer doing anything sketchy (that is, assuming they did the work they said they did - which I am quite certain they did) - is there anything at all that this could be that ISN'T gear box related? Perhaps something transmission related but that wouldn't be replaced in a straight gearbox transplant?

I am desparate to avoid paying for the gearbox to be taken apart bit by bit, and given the improbability of the 3x gearboxes with the same fault, I am hoping there are other less arduous avenues of exploration before resorting to that.

Thanks in advance folks

Edited by cornpop_2020 on Tuesday 9th November 11:02

[E-bmw]

You need to find out if the clutch & release bearing was changed at the same time.

[oakdale]

I don't know anything specific about these cars but I'd be having a close look at the engine/transmission mountings or for a missing/displaced grommet in the bulkhead, all gearboxes are quite noisy, you just don't hear it because the engine/transmission is isolated by the mountings and insulation.

I think this car will have hydro engine mounts and noise transmission is a problem if these fail.