Pioneer VSX-D811S changes volume by itself

Hello

I have a 4 year old Pioneer VSX-D811S receiver. Few days ago it started changing volume by itself, sometimes it goes up, sometimes down. It doesn't do it all the time but several times a day and it's extremly annoying. I thought it might be remote but I put it in another room and it was still happening.


Is that a common problem and/or is there any chance of getting it fixed?


thanks