air compressor rattling

Sounds like you have a problem in the A/C clutch which is what the A/C compressor pulley runs on to drive the compressor. Maybe you have a weak or broken clutch drive spring arm (for lack of a better term) which is vibrating and making the noise. If the air is cold and it makes noise whether the A/C is on or not, then the compressor must be OK. Have someone look at the A/C clutch to see if there's something visually wrong. I don't think this is a common problem. It's possible that it's not the compressor clutch at all but a drive belt or timing belt idler pulley instead. An A/C specialist or Mazda Specialist would be OK if you don't have a dealer you like. Here's a directory for you: http://repairpal.com/mazda-repair-in-wilmington-ohio