TDK1044 said:
Acceptable temperature depends on whether it's in a closed cabinet or not.
Acceptable temps are anything that are within the manufacturer spec. It really is immaterial whether the device is in a cabinet.
If a cabinet is restricting air circulation to the point of the equipment running hot -out of spec - then circulation needs to be improved. I had an old entertainment center once with a fully enclosed back (other than a slot for cable). I ended up cutting a hole near the top and installed a whisper fan.
Another possible cause of noise is an obstructed fan. I've responded to many PC service calls about noise and found the cause to be something as simple as a piece of paper stuck in the fan - think of the old kid practice of sticking playing cards in the spokes of a bike to make a "motor" noise. Besides paper, other common ones are cable ties or wires that came in contact with the fan blades when the device was shoved backwards.
Personally I don't like seeing any electronic devices stuck in confined cabinets (other than properly designed and ventilated racks). Sure cabinets look pretty but can significantly shorten the life of electronic equipment.