Let's eliminate ghosts and goblins. I can't identify your unit. Give me a make and model number.
As a test, locate the remote control window on the front of the unit, if it has one. Set it up to watch or listen to something then cover the remote window on the unit with a small piecr of cardboard. If you can't locate its infrared receiver for the remote just cover the entire front of the unit with something sufficiently opaque to block your remote. Try to operate it with th remote to be sure the unit can't see it.
If the expected problem never comes back you have a stray signal from something else in the environment getting interpreted as a 'volume up' command. Then look around for other remotes being used, wireless devices
, use your imagination. I used to have a remote-controlled space heater and my TV would sometimes shut off if I used the remote. Does the unit have line-of-sight to a nearby house? Maybe something next door (garage opener?) is interfering.
If it still happens and there are no other infra-red devices nearby you have a ghost.