I have my air compressor in the attic. I ran a drain line down through the ceiling so I can drain the water from the tank. In the winter when it is very cold and when I first start it the compressor stays running and the safety valve will release. I believe this is from moisture freezing the pressure cutout switch. I have since put electric heat tape on the pipe to the pressure switch. I have no trouble with it now, but it is 50 degrees here. In the summer I get crazy amounts of water since my garage is air conditioned. I just put a good trap before every hose reel and have to drain them a lot. The pita part is the service of the unit. In the winter it is freezing and miserable. In the summer it is so hot I wait until nightime to service the compressor.
That being said I love the compressor in the attic. The noise level is low and it is actually louder outside my garage than inside since I have an insulated ceiling. My compressor is 220 and I have a dedicated 10 gauge circuit for it. I have a glowing light switch when it is on to indicate the compressor is energized. I put this switch up high out of little kids reach. The reels are also right at the ceiling(8ft).
I used 3/4 plywood over the 7/16 plywood on the floor of my attic when I mounted the compressor. I also used very large washers under the mounting pads when I bolted the compressor down. I used liquid nail and a lot of screws in the 3/4 plywood. I made sure to hit the trusses when screwed it all down. I used lug mounts similar to what we use when mounting car lifts for the compressor mount. I predrilled the truss and set the bolts. The pita part was lifting the compressor over the studs and down onto them. This will be a pain if I ever have to remove the tank. I didn't use the lag bolts for fear of splitting the 2x4 truss.
I mounted my compressor at the very end of the garage with the fan and cooler facing the vent in the peak of my garage. I did this for the best fresh air intake, but this makes belt changes a pita since I reach over the compressor; the belt guard is between the wall and compressor. Last bit of advice. Get a very good air filter!