I have a pair of active monitors that are 10 years old. Until recently, they had been working perfectly. Suddenly they both started buzzing. I've eliminated the electrical in the home or nearby interference by trying a variety of locations within the house. This particular set of monitors has a single (2ch) amp in the right speaker that drives both speakers (speaker cable connects them). I'm thinking a capacitor in the amp's power supply died causing the sudden buzzing. I plan to open it up and look for any obvious signs of distress (bulging caps, etc.). Is there anything else that I might look at to debug the problem if the caps aren't the problem?
I'm comfortable working with power supplies; I've replaced caps in a few computer power supplies and a few Tivos.