If you rule out heat protection in the amps I would look into your power. I've had sound equipment act up all weird like, only to find after an extensive fault searching session that the voltage in the wall outlet was only 70V... Plugging into a good outlet with 230V (I live in Europe, we have REAL power in our walls...) and the problems vanished.
Heating, hot water heaters, AC etc. could screw up your voltage if there's something wrong.
...but check the temp overload protection first.