I Have a rumbling noise on over-run, which I thought was the exhaust baffles rattling. However, after using the search engine found a reference from Dave Power of 'Power Engineering' reporting that the rear diff mounting bushes can werar causing the diff to hit the underside under decceleration, due to the torque reversal.

Has anyone else experienced this on a Pre 96' UK or WRX

 

That's the same David Power as the David Power of "Powerflex bushes".

 

I have read threads that discussed knocking noises that were tracked down to worn bushes in the rear transmission carrier, so this may well be your problem. It's probably worth ringing Scoobysport or Power Engineering and asking for further advice.

Moray

 

PowerFlex and Power Engineering are as One. Two comapnies run by David Power from the Same premises in Uxbridge