Speaker volume goes down automatically on lolipop 5.1

[MERIDA]

I've set the speaker volume on max. after call the volume goes down automatically, after I set it again the volume goes down again on 20% what is the problem?

 

[dpham00]

Remove any apps that can change the volume. If you aren't sure, try to do a factory data reset and don't install any apps to see if you still have the same problem