Replacing a fan in a Power Mac G4(m8493)

I have a Power Mac G4 (Model m8493). It was free so I'm not willing to dump any large amount of money into it but when I turned it on for the first time one of the fan's sounded like a lawnmower with a stick caught in it. The fan is located behind the power supply in a 4-screw metal case. I am assuming it is the "case fan" but it seems like I have to remove the power supply to get to it so I'm not positive about that. It seems to be the 120MM size. I've read a-lot about this online and the replacement seems relatively easy if it is the case fan.
If anyone could help my out by telling me if I am correct in thinking this is the case fan and also if there is a good fan to replace it. Right now I am eyeing the Thermaltake A2018 120mm Blue LED Case Fan.
Lastly, I've seen a-lot of "how to's" on replacing the fan in the mirrored door G4 but not this version.
Any tips on replacement technique would be helpful as well.
Thanks!

Assume it is a Quicksilver as model numbers do not mean a real lot. Have a look at this link:-

PowerMac G4 (Quicksilver) Power Supply

Suggest giving a real good clean out and see if anything is obstructing the fan unit and if necessary look to replace. Not real cheap and the model may not be worth the cost however.

Exactly. I blow them out with a turbo vac.