Rear thrumming sound

[bigyin]

Hey all, looking for a bit of advice here.

had my b9 s5 ( I know it’s not a s4 but this forum was always the busier and the cars are effectively the same other than shell) for 8 months now, ever since I’ve had it I’ve heard a thrumming sound coming from the rear. Took it to Audi and my loca and both said it was not the wheel bearing and to let it develop.

the sound comes on from around 40mph and had a ‘whump whump whump’ sound (I know trying trying do describes sounds is a minefield ). It fades away at 50 and comes back at 60, the. Fades again until 70. It’s there under power or on the overrun.

anyhow the sound doesn’t really increase with speed, tho does get faster with speed. It doesn’t really show the characteristics of a wheel bearing. It’s definitely coming from the rear. I’ve done 3000miles since I got the car and it hasn’t gotten any worse, however 4 months until warranty ends so thinking I want to get on this. Anyone offer up any ideas?

google searches find me at wheel bearings, perhaps a centre support bearing?? If my car has one, or maybe the diff.?

 

[unikarl]

Have you run your hand around your tyres to see if there is any stepping in the tread pattern.
I had a similar problem on my old B7 and a change of tyres on the back sorted it instantly

 

[bigyin]

Yeah the tyres were all new so no saw toothing. It’s thrown me to be honest, I’d have bet wheel bearing originally but as I say it doesn’t get louder, only faster but almost fades away and comes back again.

 

[Pork]

Could it be the 42L5 axle alignment? I was 100% going to say tyre wear too.

 

[spartacus 68]

Not unusual to have a flat spot on a tyre, especially on soft compound tyres, but you’ve ruled that out. definately not thrown a wheel balance weight, but you’d get vibration, not noise. The way I’d determine if it’s a wheel bearing is to dismantle the rear discs and caliper so you can feel the hub with no brake friction. Some garages may look for play in the wheel, hence they are saying let it develop. There’s a few videos on YouTube with automotive stethoscopes, no idea if the trade use them?

Check if there’s disc run out or a sticky piston. Press the brakes a few times while stationary. Run the car for a few miles and then coast to a stop. The discs may be warm, as there’s slight disc and pad contact, but definitely not hot.

 

[bigyin]

Hmm, I’ll check the brakes. Cheers for that one.

 

[bigyin]

Well it’s not the brakes, both discs were Luke warm at best.
So I’m back to square 1. Someone else has suggested diff but I’m. Not convinced as I’d expect the diff to make a noise from the get go, whereas i can only really hear it above 35-40mph. Car has only done 35k.
Next opportunity I might do a front to rear tyre change over just to see.

 

[Garrett 69]

Have you ruled out worn diff mounts?

 

[aquazi]

As the tyres were all new could be they havent been balanced correctly? Either that or you have a slight buckly… eitherway worth getting them off and checked by a tyre shop.

 

[bigyin]

Yeah I think I’ll get the wheels and tyres checked out just to rule it out.

 

[pagenotfound]

could it be some trim flapping? rear bumper, wheel arch lining or under body protection - that sort of thing?

 

[K44WMY]

I might have this same issue on my b9 s4. It drives me crazy as i am very pernickity.
Mines is more like a qua qua qua noise. Sounds like a duck stuck in my wheel arch. Mines comes from front wheels area. Noise gets faster as i accelarate. Cant hear it at high speeds. But when cruising in town as im passing parked cars the noise is more as it hits of the cars and can hear better. When brakes are pressed noise seems to go away. Checked and replaced tyres 3 times and even replaced discs pads 3 times so i know deffo not them. Any help?