I got my hands on three ALTO MAC 2.2 amps for free. They are all broken in same way. When they are powered they start making this sound which I can only describe as a kind of surring noise. Otherwise they seem to work normally. I'm pretty sure it's caused by broken cooling fans. Has anyone got any experience with these amps? If you know how to replace/fix the fans or have the same issue please tell me I don't want to open them without knowing what i'm about to do. Also, I don't have anything that can manage this much power, so I think I will sell them if i can fix them. How much do you audiophiles think they are worth?