First, is it snapping or humming at frequency that changes with engine speed?
If so, it is likely ignition or alternator. Make sure your hood is grounded well (should be on a Volvo) then look for bad plug wires or a failing alternator.

If it is random static, try hooking a different antenna (any piece of wire) directly to the back of the radio. That will help narrow the problem down to radio, antenna, or antenna lead. Try the same radio in a different car.