Buzzing electrical sound - Help!!

[Boxstertom]

Hello all
I am a newbie to this site, but have recently purchased my first Boxster (2.5 '97 Metallic black with grey leather) and absolutely love it.

I have a couple of embarrassing newbie questions.
On day 3 of ownership, I started the car and there was this buzzing electrical sound coming from down near the fuse box (Right hand drive as I'm in the UK so fuse box is also on the right). And on the centre dash, the light on the switch for the mirror defrost (which I actually thought was rear window defogger) was also flickering. The buzzing got a bit worse and higher pitched and sounded like (for want of a better phrase) a wasp caught in a matchbox or stuck behind your curtains and finally stopped. Now the light on this switch is sometimes on and then goes off again and vice versa but the button itslef does not work anymore.
I am assuming the noise was a relay of sorts that went mad and died.
The fuse for the mirror heater (D2) is still OK. I even tried a spare.
So.... to get to the point.
Can someone tell me where in the car I can find the relay for this and also whether I can just buy a relay from a general automotive store or does it have to be a Porsche one?
If it can be general then what is the spec I need to be looking for.

Thanks for any help and advice you might have.
Cheers,
Tom

P.S. Does that vent near the back window actually blow air at he back window??? And if so, what button activates it?