Darren,
I once mounted a compressor above a ceiling. The boss went potty because he couldn't hear himself think, and I had to drag it down again. I even built a frame to hold it off the rafters. The ceiling acted like a large speaker cone. Bouncing the sound up to the factory ceiling and then down again onto the office block.
I have also mounted one way up on a wall in a factory, and it worked and sounded a dream. So the only thing to do would be to suck it and see.
If I could make a suggestion that would be a lot quieter. Build a box outside and put it in that, but feed the induction pipes from inside the shop so that it will be sucking mainly nice dry air. Also it won't be adding to the heat load in the summer.
When I feel more up to it, my compressor will be going out back, if only to stop me jumping when the damned thing kicks in.
Now is the time to definitely consider 3 phase, while you still have access to bury everything in the walls.
Having 3 phase is as good as printing money. You can usually pick up 3PH machinery much cheaper than you can 1PH.
I have no idea of the cost though, as your place would need to have it piped in I suppose, unless your mains is 3PH already and they are tapping 1PH off it.
John
