japtorque

firstly how can i check my diff bearings? when the is car rolling around 40 mph u can really hear something grinding away quietens down a bit when u dip clutch or put un netural but deffo sounds like its coming from rear of the car checked wheel bearings etc they all seem fine no play or anything so i think its my rear diff any way of knowing its knackered?
also what diff will fit i have a 99 uk impreza

was offered a 95 wrx diff but didnt want risk buying it
all advise welcome