slight rumbling noise when suspension compresses - CV joint? Gearbox?

Cloth Ears

Cloth Ears

A2OC Donor
Hi,

I've noticed a rumbling sound (a bit like tyre noise, but lower in frequency and not as loud) when the car goes into a dip or over a crest (ie, the suspension compresses or un-compresses a bit). It's not intrusive, but I can't un-hear it and I want to be prepared for any potential work. It doesn't seem to be anything that is apparent during cornering, as far as I've noticed.

I wondered about CV joints or diff, but the garage I use (Awesome GTI) says they look OK and have pointed the finger of suspicion at the gearbox. The gearchange has also got more notchy, so they may be right. I've asked them to adjust the gearchange mechanism, which helped a bit, but it's still notchy, and some gears (eg third) are becoming a bit tricky to select, some of the time. Engine temp doesn't seem to be a clear factor in whether the gears are awkward or not, though. I had the gearbox oil replaced at the last service due to this and they said there was some evidence of rust in there.

So I'm thinking about whether it's time for a replacement gearbox, or a rebuild; but I'm also loathe to have that work done if it's not the issue. So far, it's not got markedly worse, and I'm still using the car (albeit rather less due to working from home) but I don't want something to let go expensively, or strand me somewhere.

Any of this ring any bells with you guys? Anything I should point the garage to looking at - it's going in for service and MOT in a week or so.

Thanks!

Steve
 
Have a look at the rear shock absorbers. The upper covers can become detatched from the bump stop and drop down the shocks and rattle. The heatshield near the offside driveshaft could be loose, just not much to go on. The gearbox could benefit and drain and refill of gearbox oil.
 
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I used to occasionally get a low frequency groan through the frame after speed bumps or in road depressions that caused the car to squat a bit onto the rear suspension when there were passengers or cargo in the back seat or boot. My gut instinct was that it was the rear subframe bushing on driver's side - it looked ropey and was replaced a fortnight ago (along with the rest of the rear suspension except springs) and I've not encountered the sound since, but also the rear shocks, spring seats and other noise-absorbing parts were done at the same time.

Can confirm having driven some country roads with 4 adults in the car the other night that the groaning noise from loaded rear suspension has now gone.
 
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Rust in gearbox and difficulty selecting 3 Points to the selector tower Bushes and seals. Also check under bonnet drainage.
 
Thanks, that's useful steer - I'll pass this on to Awesome when I go in. A bit disappointed they've not already considered this, if I'm honest. I did check that water catching cup thingy was properly seated, and it is. There's no obvious indication that water has been allowed to get to the tower, but I'll ask them to check it carefully.
 
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