The fella Beenthere had a interesting one about the fan blade cracked. The only other thing I was thinking was as the fan blade accelerates/decelerates it flexes a little. I know this becuse of course I have never put a condenser fan motor a little too low on the shaft, hahaha.
I did one and it flexed enough to tap on a pinch off tube below as it sped up. pulled the disconnect as fast as my a** could get to it. maybe on the decel it is flexing up and tapping the cage. dunno or maybe a set of wires hanging down. (around here it is the reversing wires tie wrapped to the cage that break in 120 degree heat and fall in)
REALLY annoying - especially as it's so cowardly as not to make the noise when I get outside to look at it!
The blades aren't cracked (checked that). I don't know if they can flex enought to hit the refrigerant pipe (I doubt it as the unit only makes the noise when the fan is going slowly - not enough air resistance to flex them that much) but who knows? Will post the solution if and when it gets fixed (the yokels out there in the mountains only work weekdays, and we only go up there at weekends).
Well, turns out is was the condenser fan motor making that noise. When it starts up and slows down, it makes a metallic clanking noise that goes away when it gets up to speed or stops. The AC guy said the motor is going out and offered to replace it but also said it probably has a year or two left in it yet. I'm holding off in case anything else goes wrong, possibly making a changeout the more effective route.