Noise is driving me crazy!
 

Recently changed gearbox on my blob sti as the old one was beginning to crunch into 4th gear. Car was parked up since October and gearbox fitted in December.

As I was driving to mot I noticed a grinding noise from the rear when lifting off, which would go away if I dipped the clutch.

Long story short but another gearbox, 2 prop shafts, 3 rear diffs, 2 sets of drive shafts and 1 rear wheel bearing later and the noise STILL exists. Brakes all cleaned/inspected, absolutely no witness marks on anything, even poly bushed the rear diff mounts, outriggers etc.

It drives fine, changes gear fine, just a bad grumble/noise from the rear once speed is over 30 mph and you lift off.

What am I missing?

Tyres are all less than a year old, Dunlop Sport Maxx.

Check the backplate on the rear , rust can build up underneath them , push the backplate away from the hubs , and the disc can rub on the lip of the backplate , could be touching just enough to make a noise under load
Check the backplate for marks , it might not be obvious straight away
Cheers Ian

check the bushs from rear frame to chassis, had this same problem and changed gbox made no difference, the bushs where worn out and frame was vibrating on chassis on liftoff throttle only in 4th gear over 30 mph

Thanks for this mate, definitely going to be the next port of call as theres not much left to look at. It would actually make sense as i've had a clunk on gear changes from the rear but only notice it when i'm not running my back seat.

Well I've replaced the following and STILL have a noise when engine braking above 40 mph
I've done around 500 miles in the car and the pattern is basically a grind/vibration type noise at the rear when lifting off in any gear over 40 mph.

I've had the following replaced or checked
3 x 6 speed gearbox
2 x prop shaft
3 x rear diff
2 pairs rear drive shafts
New rear cradle and bushes
New trailing arms, lateral arms and bushes
New rear diff bushes and outrigger bushes
New wheel bearing on drivers side rear.

Literally the only parts left are the passenger rear wheel bearing and the 2 bottom bushes where the trailing arm meets the hub

Checked the back plates for swelling and witness marks and cant find anything

I've taken 3 technician/mechanics out in the car and none can pinpoint it.

Crazy stuff!

Have you put the rear wheels on the front yet?

Is it a cement mixer type rumbling noise on the overrun when you lift off?

If so, it may be your clutch. What clutch are running?

Did you ever find the cause of the noise? I have exactly the same thing and can't find whats causing it. Recently changed outrigger bushes to poly which has made it worse.