Would be a good idea to first check all cable connections for cleanliness & tightness of fit, including your AC power. Also wiggle things a bit to see if you can locate any defective / marginal connections & while you're at it, go over everything once again with Kontact cleaner & pipe cleaners (you know the drill - right?). Refer to Galen Carol Audio site advice in that regard if you're unfamiliar.
http://www.gcaudio.com/Archives/howto.html
Failing that you also you might take a peek under the covers for any loose connections, IC's not firmly seated in sockets, etc.
http://www.gcaudio.com/Archives/howto.html
Failing that you also you might take a peek under the covers for any loose connections, IC's not firmly seated in sockets, etc.