Hey guys, I'm having the exact same problem with my 3500. Seams to me it's broken bearings, or some other mechanical problem in the fan itself, since im not expieriencing any electrical, only a whining/ grinding noise. A temporary solution for the problem in my amp is wiggling the head about a bit. Since I'm getting fed up with that, I'll be replacing the fan. In case anyone of you is planning the same thing, It's important to know that you'll have to you get a 24v fan, as the more common 12v variety will probably fry upon impact. Another possible problem is that the fan in my amp is rated at 3.5 watts, the normal 24v fans available in PC shops only go up to 1.7 or 2 Watts max. I'll try it anyway, and post the "results", if any of you are still interested.
