Update: I finally traced the noise my neighbor's AC was making, and it wasn't the compressor
I was on my porch in Reno last Tuesday and that grinding sound hit every 6 minutes like a clock. Turns out a loose flex duct was slapping the blower housing, not a failing unit, so the $400 repair quote he almost paid was junk. Anyone else run into a contractor quoting a whole swap before checking the cheap stuff first?