Problem with Supratek Chardonnay

I have owned my Chardonnary since early in 2003. Recently I have noticed that the sound breaks up in one channel when there is significant emphasis on high notes. This problem switches channels when I switch my preamp output cables but not when I switch input cables to the preamp.
I have tried switching tubes but this does not cause the problem to switch channels. I have cleaned my input and output connections. So now I am wondering if I have bad capacitor or some other part going bad. I would appreciate any input you smart folks can provide.