Testing a psu

[Banzai_Joe]

Hi all,
just had to take a psu back to the shop cos the case it came in, well, after i'd built the rig, the psu made a noise like a tractor, so i put a spare i had in and all was fine.
I took the offending psu home and put it in my spare rig, it acted the same with a nasty motory noise.
So i takes it back to the shop and the guy hooked it up to a kettle lead and used a paper clip to connet two wires together in the 20/24-pin mobo connector. The psu burst into life but was silent as smooth.
They claimed i may have gotten cables in the way of the fan, but i know i didn't (certainly not twice). They swapped it anyway, but i'm thikning, this isn't really a decent test is it. It just test power to the psu surely?
My theory is that once everything was connected ,cos the psu is faulty, it didn't have enough juice to power all the components and keep the fan running smoothly. Is this possible?

Your opinions, as usual are appreciated.

 

[Rich]

Its not a thorough test as you say, merely a test that proves it turns on, not what it will do under load. The fans are no doubt thermostatically controlled, and run at low RPM when under little load, and increase under load. The Vibrating may only be above a certain RPM.