My old AC unit is probably from the 70s or 80s. It's been rattling A LOT, probably forcing my neighbours to close their windows at night. So I called Belyea to come look at it, and yes, there was a problem with the fan shaft which was causing the rattling, $900. Ok, let's do it. We scheduled the appt in 2 weeks, but a heat wave was coming, so in the meantime I opened it up just to see what I could see, to mitigate the rattling in any way possible for now, and...I found a loose nut and bolt that was supposed to clamp down a bracket. I tightened it up, and...quiet AC unit. No rattle. Cancelled Monday's service call.
Lesson: don't let your guard down, even with the highest rated Homestars people. I almost spent $900 for a job that required $0 in parts and 5 minutes of my own labour!
*NOTE:* They were actually very nice and professional! And no doubt they have a high standard on those points. They also offered to reimburse me for the original service call.