I haved owned this head, and , if you are running into 8 ohms, it does have a tendency to run out of head room pretty quickly when pushed. I don't know if the fan making noises would lead to overheating, but I would think the head would shut down before losing volume. When I owned it, I never noticed the fan at all, or the head getting hot. Is this what you are experiencing ?
R.I.P Duck Dunn, 2012.