This doesnt happen very often, but when it does it's a guaranteed call back sometime down the road. Customer calls, says unit is acting up or making noise of some sort, you go out to check/diagnose a problem and when you get to cust house the damn things not doing it anymore. Just basically looking for different strategies for this problem, or does nobody else have this happen to them? I'm only 22, been in the trade for 4 years, yes i do check for obvious things that could be going on, such as belts, bearings, dirty filters, flame rob mA, propper combustion, etc. So any input would be appreciated!