Could be lots of things, a power issue, a ground problem (bad connection), or something failing.
Some basic trouble shooting:
Is the buzz coming from only one speaker?
If yes, does it move with the speaker when you swop them?
If yes, the problem is with the speaker.
If no the problem is upstream.
No, the buzz comes from both speakers..
Turn off all source components and unplug them from the inputs to the amp. Sill buzzin'?
If yes, then the problem is probably with the amp or your power.
Try a different power circuit, a power filter, etc.
If no, hook up one source component to the amp.
A battery powered source (ipod, recorder, etc) would be ideal. Buzz?
If no attach and power up your other source components one at a time,
testing each to see which introduces the buzz. Check all your connections.
Also might check to see if the buzz changes when you move the cables or components around (RFI interference) you might find what ever is causing the problem, a particular position or cable routing that effectively eliminates the noise, try different cables that are more immune, etc.
Terry, the
varistors in inexpensive surge protectors can degrade and stop offering effective over-voltage protection over time but won't filter out noise in any case. Unfortunately I don't know enough about AC-line filters to recommend a one for your application.