I have a 6 speed fitted to my 94 wrx and have noticed a knocking/thumping from under the car on occassion, you can even feel it through the floor! Could this be the gearbox moving about? Would it be worth while fitting an uprated gearbox mount?

Nathan

 

Yes.
Call Mark at Lateral Performance as he sells the Prodrive ones. About £70 ish.
Graham
(some times on ebay too!)

 

I've got an uprated mount fitted to a MY00 with 6 speeder, and i still got an occasional knocking sound when pulling out of a t junction.

It turned out to be the exhaust hitting the propshaft carrier bracket.
I ground away the lip on the bracket and it seems to have cured the problem

 

I had that on the over run with my 3'' decat system on a 5 speeder as I couldn't get more than 5 mm clearance to the center bearing carrier.
Graham