Saab: Radio and trouble whooting a buzzy noise.

Hello all
Has anyone repleace the radio in the 9-3 with an aftermarket one? Since the
radio is tied to the computer display system, how is the computer display
system effected by the change? I know that I would lose the steering wheel
controls, but what else. Does anyone know who may have a monting plate for
standard size radios?

A little trouble shooting:
When I turn the car off I continue to here a buzzing noise from behind the
radio/glove compartment area. I don't know how long it says on for. I am
usually around the car for at least a minute for which I still hear it, but
it stops by the time I return to the car. I also hear it when the car is
running. I will not discribe the noise, but I thought someone may know what
would be in that area that could buzz and why I would still hear it after
the car turns off? It is not the radio, still there when I turn of the
climate control unit. Any thoughts?

thanks
keith