A few years ago I had an Aguilar TH350. Great amp, but the fan operation was odd. The fan would come on after about 20 minutes even is the amp was being used at very low volume or even just idling. I would assume that the amp would get hotter the harder it is driven and at low volume it would not need the fan. Am I wrong? Do all class D power amps act like this? Do they build heat and need forced air cooling at all volume levels?