Power supply fan usually hums along just fine. Every few days, after coming out of hibernation, the fan seems to go into overdrive mode and gets VERY noisy. Not a rattling/wobbling fan noise, just seems super fast. Do these things have 2 speeds? I really dont thinks its a hardware fault, as the fan is brand new. Computer only 4 months. Quiet right now.
The PSU fan normally runs quietly all the time.
If you are certain it's the power supply fan that's noisy and not the case, or processor/heatsink assembly fan, as the system is less than a year old and has a warranty, best you contact Dell's Technical Support and request an replacement TFX power supply.