whats an average sort of price for a box recon.

my box works fine, till giving some beans. some times clanks from 3rd to 4th
but driving normal is fine. no crunching ect

but letting off the throttle, has a sort of gratty wrine
its a p1/sti box

it may be something else, as i know alot of these scoob boxes make strange sounds.

but just after around abouts price & best place to have this sort of thing done