clanky horrible tone out of my mark IV

[MetallicaFreak65]

My friend left my mark iv running on standby for about 24 hours the other day, and when I went to play the lead channel sounded extremely clunky and clanky and it is really flat is it my preamps?

 

[zebpedersen]

I used to leave my Subway Rocket and Mark IV both on for ages and never had any problems - possibly a tube happens to have gone in that time? It's not a great idea to leave your amp on for extended periods of inactivity (what's the point, after all) but I wouldn't imagine that leaving it on by accident like that would have damaged the amp's internals, except possibly a tube, which I would say is still coincidental.