There may be a problem with the fan thermal control circuit in your Antec. Does the fan speed go up when heat output increases, like when burning CD's or gaming? Or is the fan just running full out all the time?
Does your system have other cooling fans? If not, the antec fan may be running on high for a reason....
If the thermal control is not working and the unit is within the warranty period, contact your vendor for an exchange.
I have a 300w antec and an enermax, both are very quiet, I really can't hear any difference between them. In terms of build quality, the Enermax is easily the best I've ever owned...