dude...

if you reckon you have the skills to fix it, then get out there and do it. asking questions on a text based forum isnt going to help. you havent, and cannot give a reaonable description of this apparent noise.

ill give you a hint, the rear diff has absolutely nothing to do with your stereo. (<---- read that again, just so you are clear)

pull everything appart and put a new pair of brake shose in (cuase they are cheap, remember to adjust them properly). check the wheel bearings are intact while your there, but since you reckon it doesnt do it all the time, im gonna guess it isnt that.

there really is nothing else in the back of a ke70 that has the potential to make any noise. appart from the diff centre, but you will know about that if it is playing up.

now off you go! less typing on keyboards, more swinging spanners and getting covered in brake dust.