Learned the hard way to always observe first on tricky calls
Got a call for a unit making odd sounds, homeowner pressing for a quick fix. Did my usual checks, pressures and connections all looked good. Decided to just sit and watch the system run through a few cycles. Took about half an hour, but then I spotted it. The noise only came when the indoor fan started up, not during compressor operation. Found a cracked bracket on the blower assembly, barely visible unless you wait. If I had rushed, I would have blamed the compressor and wasted parts. Now I make it a rule to spend extra time just observing before I touch anything.