Hissing sound from right speaker

I fired up the system last night and began listening to a LP that sounded like it had horrible surface noise. Upon investigation, it was not the LP, but a loud hissing noise coming from the preamp. When I muted the preamp, the sound went away. By changing input selector (LP, CD, etc.) there was no change. It is a Klyne pre plugged into a PS Audio 300 power supply.

Any thoughts on how to trouble shoot this issue?