Loss of volume in right channel


I've noticed that my system is intermittently losing volume in the right channel. Usually starts out fine when the system is first turned on. Plays well for a while. And then the right channel will suddenly cut partially out (never a complete loss of volume). Then it will come back again. Also, I occasionally hear a sizzling noise in that channel.

I checked my source equipment, and the problem remains consistent with the right channel, so I'm pretty sure it's not my CD player (most often used source). Speakers are in good shape. Swapped pre-amp/amp cables, and problem remains the same, so it's not a cable problem. I'm thinking the problem is in the pre-amp, which has had a couple of "open" circuit problems in the past. Any thoughts ? Thanks.
bothrops1b81
Most-likely it's an amp.

First off we need to know what amp you have (tube? transistor?)

If you have a tube amp you'll definitely know it's a tube(s)

If you have SS amp and can reach an output transistors, you should check-compare its temperature on different channels.

Replacing transistors in SS amp is a-bit more tougher and may require tuning and matching. Often you would want to replace output transistors on both channels especially if you can't find right replacement.

If you connect only faulty channel, you may hear clipping even on low volume while the one non-faulty will play OK.
Pre-amp is a 13-year-old PSE Studio SL. Amps are monoblock PSE Mk Vs. All solid-state.
I had a similar experience with a channel going out occasionally. It would actually come back on when I would walk near the amp and back off when I walked away. I swapped cables and still happened. Finally bought new cables and problem went away.