Sorry to hear about that. Are you sure the noise is coming from the PSU fan and not any other component? You can stop the fan by hand for a moment to check that. When you say that it's more noisy, what do you compare it to?
Yes, it's coming from the PSU. I dont hawe the system here now, i've build it, now my friend use it. He says that it is pretty quiet, but i dont think so. Maybe i'm just a little bit more demanding.
There was no noisy fans in that PC, just one Noctua NF-P12 @ ULNA (900rpm) and one regulated 800rpm Noctua NF/S12.
The sound was like a hum from the high airflow, coming right from the PSU. I've stopped the other fans, it remains.
In other system that i've build, with E2160, 1xHDD, 2xDDR2, Gigabyte P35-DS3 and ATI X300SE, this PSU was deadly silent. Even with a small upgrade (OC to 2.6GHz, 7600GT, 4xDDR2), it is still inaudible.
But the thing is, that for me that system was loud, but my friend was excited about how quiet it is...
These Seasonic PSUs are the quietest that i ever hold in my hands, but i think that when it comes to high power draws, it can be noisy like other regular PSUs...
Oh, and the fan inside is ADDA i think, just like other Seasonic PSUs.