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: 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.
It's now switching to another unused input, aux2. There doesn't seem to be any pattern to it.
If it has a remote, try taking the batteries out of the remote (to eliminate the remote control as a cause).
Tried removing the batteries from the remote. For a while it seemed to work, until the amp switched inputs on me again. Sure seemed like a plausible cause though. Thanks for suggesting it.
FWIW, my Sunfire was doing that some time ago, so I checked the Auto Select setting; do not know if MF has that feature. It was ON, but even when I turned it OFF it was still switching inputs. Anyway, in the end I had to upgrade the software and perform a software reset to stop it from switching. All okay now.
Well, here's another idea. Please understand I don't know how the remote sensing feature works on the MF gear, but if there's a sensor window cover it.

If eliminating the remote quotient doesn't address the problem, and if you've already powered the unit off and on, then I'd say it's time to send it off to an authorized repair facility.
I just power cycled the unit and covered the IR port on the front with a post-it note. Just waiting to see if this works...
Any chance of a nearby neighbor using a remote on the same frequency?
An electronics designer told me that sometimes AC filters can boost the line voltage a little bit to make them sound better... but if your line voltage is already on the high side (mine is) the extra boost can cause op-amps to bug-out.

Instead of plugging your integrated amp into the AC filter, try plugging it directly into the wall and see if that eliminates the auto-switching. If not, then it might be time to send it in for service as Tvad mentioned.
Thanks for the suggestions. Since re-cycling power, the unit has not changed input selections. I still have the IR port covered too but I plan to remove that if I the good behavior continues.
Interesting development. The system changed input selections after I removed the post-it note covering the IR port. It does this after some time just playing. Seems like something is triggering it. I'm going to try removing the batteries from the remote and removing the post-it note from the IR port.

Must find gremlin.
You're doing a good, systematic troubleshoot.
If you have an fluorescent light near the sensor it can cause the problem.
I removed the batteries from the remote and left the IR port on the amp uncovered. The amp repeated the change-- selecting another input with no action by me. I then looked for another IR source that could be causing this and remembered my IR-to-RF converter.

This device effectively extends the range of any IR device by inserting an RF transmitter into the battery compartment of the remote, and then duplicating the IR codes to the hi-fi unit. I've had it for many months and forgot about it. I also am not using it with the amp, but instead use it with my Squeezebox player, so the converter is only sending SB IR codes.

The IR extender has options to transmit on 3 frequencies, so I selected C when the unit had been on B. It's been a few days and no repeat of the issue. Amp seems to be working normally and I can still change Pandora selections from anywhere in the house.

Odd that I've been using my system with the extender with no issues for many months and only recently did this issue appear.

Here's the Amazon link for anyone interested:

Thanks for everyone's help and encouragement.
It appears you have found the solution. Way to go!