Buzzing rear view mirror

My interior mirror is buzzing at certain speeds - very irritating. It's slightly loose which is why it has started and (as usual) Haynes is no help about tightening it up. How can I get at the fastenings to tighten the mirror on its stalk?

Cause of vibration, cure upcoming... 

It looks like the cause of the vibration is a dodgy wheel bearing. Since it's going in tomorrow, I will ask for the mirror to be tightened too and post (if I can) how this was done.

Hi Simon, If its like the early V70 then you take the interior light lens out and you'll find two screws to undo the trim section . V70 has two slotted screws holding twin break away wires (to give in the event of an accident). These screws can work loose.

My 240 did this from around 18,000 miles, and still does. It isn't the mirror that's the problem, it's when the car flexes a certain way the top of the windscreen mounting can vibrate very slightly against the body. It took me years to discover the actual cause, as yanking on the mirror restores the roof to it's correct position, and the buzzing stops. It's probably only a sixteenth of an inch of movement, but it produced the annoying buzz. I only mention it in case the mirror mountings don't fix your problem.