ReadyNAS 316 case fan spec

Hi

does anyone know a good quiet replacement fan for the 316 ?

 

Its 120mm and has 4 pins, but is not a standard PWM fan - I know because I have one of those and tried it, the plug is subtly different. The original is a delta fan, quite a common model, except for the plug on it. Its quite noisy though when new, and even more so now the bearings have gone.

 

Anyone sucessfully replaced their fan and have a make/model number to share ?

thanks