Very.

I had one in my old Digital Audio. The noise it made was half the reason I sold the system.

I had one in a QS2001. I didn't really notice any increase in noise, but the QS is already pretty noisy. Unfortunately, the machine self destructed for other reasons after two days. I REALLY notice now how quiet it is with only my PB running!

Its so noisy that I wish I hadn't purchased it. I had to remove the two little fans that they give you and put on an 80mm fan. Its a lot quieter now but I voided the warrantly. I dont really care as I wont be purchasing from them again.

Are all the processor upgrades noisy, or is it just the higher speed dual processor ones like the Giga 1.8 dual?

I work in a server room all day, so when I come home I really don't notice the noise of the fans on the dual 1.8 I have in my Digital Audio... but I would warn you that the upgrade over-heats easily because it's a dual 1.4ghz overclocked to 1.8ghz. If you're like me you've got a lot of internal drives. I had to buy another fan to hack the poor airflow in my case.

All I can say is .... you poor b*st*rd.

What's that??? What did you say? I can't hear you over the ROAR of my fan?

I had one of thier 800mhz upgrades, and the fan on that was so noisy I ended up selling the machine to my wife's cousin on the cheap.

You sold a machine for less than it was worth to avoid replacing a $5 fan?

Have you heard of the Pratt and Whitney J58 turbojet used in the SR-71 Spyplane?
It's like that, only a bit quieter.

I've got a Maxtor U160 that will take half your life's hearing left in about a 1/2 hour.