First, thanks to everyone who has offered their help and expertise on this, I'm new to tubes and need all the help I can get. I played around a little bit last night and I could reproduce the pop when I plugged and unplugged my phono stage. The weird thing is, it didn't happen every time! I have no idea what it could be, does the problem lie with the amp itself or my wall outlets, or both? Again, this is a new problem, only within the last week. It's strange because I was hearing it on its own, withough plugging or unplugging components...only today it happened when I plugged/unplugged my phono stage.