Integrated changes input selection by itself

Hello. My MF A3.5 has started changing it's input selection to Tuner ALL BY ITSELF. It does this intermittently. I have only two inputs connected, CD and Aux1. There is no other source for the amp to play, yet it switches to Tuner every once in a while. It plays normally, and then jumps to the Tuner input. I then select the Aux1 or CD input with no effect other than I missed a few bars of Jazz. Everything else seems to be normal.

I've had the amp for several years now, and purchased it as a demo from an Audiogon member. This behavior of self-selecting to the Tuner input is a very recent phenomenon.

Here's my system: http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1187457873&view. I've traded up to the Quintet for power filtering and upgraded the speaker wires to Kimber 8PR, all last year.

I could not find any posts with this issue so I'm asking this community for comments and suggestions. Thanks.