I've been going through the pages of this topic and it's bugging me because maybe I'm the next one suffered a failure on the PA5.
I found that it heats up after 30 minutes of use, regardless of the volume applied.
I don't have a problem at the moment but I prefer to unplug it from the mains when not in use.
P.S: I fooled around once, I unplugged it from the mains, forgetting to flip the switch to off before, and I heard a funny tone in my columns. I specify that the volume was at 0.
I tried to recreate this tone with audacity, here it is:
https://sendeyo.com/show/cdd00461c8 password : 1234