Our new Ashwood Builders home has 2 AC compressors mounted outside on a small concrete slab that is connected to the main foundation. All the other homes in this new neighborhood that I've checked have a small gap between the compressor slab and the foundation. Even though the new compressors are quiet, we get a loud humming or buzzing sound inside the house in the room closest to the compressors. I'm guessing that if there was a gap, the vibration would not be able to resonate into the room. I'm wondering if this was a builder's mistake? I'm wondering if there are any regulations in residential building codes regarding this that I could use to persuade Ashwood to fix it? And if not, I'm wondering if a typical hand-held circular saw fitted with some sort of blade for cutting concrete, would be powerful enough to cut the gap myself?

I would definitely complain to the builder. Code and the building inspector may not be much help.

You should be able to cut the slab depending how thick it is. You may want to rent a heavy duty saw rather than abuse your own. Just tell the rental place you need a saw to make a concrete cut.

Thanks, I will probably request the builder to fix it. But if they refuse, before trying to cut a gap, I might first try lifting the compressors up an inch, and slipping some kind of all-weather heavy-duty rubberized insulation underneath... hoping that will reduce the vibration. But if the compressors are actually bolted to the slab (are they usually?), I will be faced with cutting the gap.

My compressor sits on a plastic HEF-T-PAD made by Hefco. It came with the Bryant unit. It is not bolted down, and neither was its predecessor. You can move them around a little, the copper tubing has some give. Mine is fairly solid now that I have rigid conduit running to it to replace the flex the dog chewed up.