it could be valid or unvalid, depending on what he was doing
if he was setting the fan speeds all the way up, that would obviously make noise
if hes just running too many heavy programs at once, then the fans will obviously be at full load, and the guy just doesn't understand computers
if it's doing it by itself you probably did something wrong
maybe it doesn't have enough airflow, or you're using a weak cooler with a warmer processor
the fans might not be installed properly, or they are just bad fans overall
so couple things to ask him:
did he change the fan settings?
how many programs is he running at once?
did he tamper with the computer at all?
either way, if you're making money from him, then you could just take it in and easily fix it