Amplifier temperature control

I have two amps in my system; one of these, my Rogue Audio stereo amp runs pretty cool and doesn't seem to need cooling beyond some cross ventilation. The other is a B&K 150wpc AVR307 receiver which does run pretty warm at 130F plus at the top of the cabinet.

I bought a used first generation ATM Coolstack but it only operates with the transducer unplugged which means that it is always on. This is a problem because it is noisy and very apparent when the amp is not in use, and even noticeable when listening at low volumes.

Is there a temperature limit that is generally thought to be a potential problem and is there a cooling fan that works without the fan noise of this unit?