Are "silent" CPU fans worth it?

My PC gets louder the more I ask it to do. I'm running Windows XP Pro on a 2.93 Celeron chip on a ECS motherboard with 2 GB of DDR ram. When I run multiple taks it gets louder and louder. I was thinking of replacing the PSU. Are there quiet PSU's on the market? What I have now is the bottom of the barrel cheapie PSU. My CPU fan and heatsink is reletively clean, so I don't think that is the problem. I upgraded the CPU fan to a Coolermaster "silent" fan when I built this thing. My impression is less than satisfied with that. Any suggestions would be appreciated. Thanks.