I actually contacted Antec on this matter, and for the same or similar Neopower model.
My gripe was that I wanted greater CFM throughput through the PSU, and people had told me they only show their PSU fan running at 1,400 rpm. Antec told me that the fans were thermally controlled, that they run to a maximum of 3,000 rpm, but replacing the fan would not resolve my problem and preference.
In your case, we have a different issue. Technically, opening your PSU will void its warranty, and there are some few "electrical risks." But it is done by many. I would suggest first that you remove the PSU from its case and attempt to lubricate the fan bearing without disconnecting it. On the other hand, it may be just as easy to find a 120mm fan -- from either Antec or another provider with the same amperage rating -- and just replace the fan.
As for the warranty -- "Don't ask; don't tell." And as for the risk -- be careful.