Cary SLp05 Preamp noise

recently I encountered a buzz in my right channel and after usual ground loop investigation did not reveal the problem, I looked at maybe a bad tube in my Cary preamp. The tube tester did not reveal a defective tube but what I noticed was that moving the tubes around in the sockets would eliminate the buzz. I'm using Sylvania 6SN7's and this continues to happen. Pins look clean and shinny and I have cleaned them superfiscouly but the problem seems to pop up every once in a while and I'm wondering if there is something that I don't know about pin and pin socket fit up. Can anyone shed light on this situation?