Need help diagnosing clicking sound

I have a passive subwoofer powered by a bridged Adcom 535 driven by an active x-over. I drove the amp/speaker hard and now I'm getting a buzzing/clicking sound. This sound occurs when I'm not sending any audio signal through the system. It sounds almost like a buzzing sound of interference from a refrigerator. (I checked, that's not it.)

The sound is not very audible when the x-over sub gain is set to 1/2, but is VERY audible when the x-over pot is on full gain. I don't know if I damaged the amp, the electronic crossover, or if I just need to clean some connections, etc. Any advice on how to diagnose this?

Dan: Can you provide one other bit of info? Where do you hear the clicking -- does it seem to be coming from the amp, the crossover, or the speaker?
Ah, the clicking sound is coming from the passive subwoofer that is hooked up to the Adcom. If I had to peg the freq of the clicking, I'd say about 3000Hz, but on a rhythm of 40Hz. Hmm, I'm going to check the warble tone generator in the active crossover. Maybe it's on. I don't have any cables hooked up to that part of the x-over, but maybe it's jumping connections/crosstalk, etc.