THE MOST ANNOYING KNOCKING/VIBRATION NOISE IN THE WORLD!
 

This has been driving me crazy now for about 4 weeks and i have no idea what it is.
I have a 1998 uk impreza turbo 4 door

Everytime you change down a gear (most noticeable from 4th to 3rd and 3rd to 2nd) i get a bad vibration through the car. It sounds like its coming from below the rear passengers door behind the drivers seat. It is really noticeable. I have looked at everything underneath and it all seems fine. i have tried shaking bits such as the exhaust but i cannot make the noise. I have also taken the door off and shaken that etc...!
I simply do not know what it is and was kind of hoping you guys may know or have some suggestions for what it is.

Please help

are all the bolts on the gearbox mounting on securley?

funny you should say that - I havent checked but i had a bracket made up to bolt to the downpipe to the gearbox and when i was shaking the exhaust i nooticed that the whole gearbox section was moving (imo more than normal) does the gearbox often move alot? Are these bolts easy to get to?

I have a clunk when mine changes down sometimes in the same sort of place i am thinking.
Started after recent track day :(

I though mine was maybe the drive shaft but will also check this!