I just want to share my experience.... I have a thermaltake volcano 9 with my overclocked Athlon and if i want to run at high vcore, my volcano need to run at max speed (5200rpm) and it's very loud. The trick i've done is to switch the fan on the volcano heatsink to a Sunon 80mm ball-bearing fan, who run at 3000rpm, just to try... Also i've took the removed volcano fan and and use it like a rear exhaust fan, and i can use the fan speed controler to reduce the noise at the level of the rest of the system. The result is that the sound go from 49db to 30db and my temp are lower then before. From 40C to 35C idle and from 58C to 53C full load. I was at the point to purchase a Thermaltake silent boost at 40$ CAN, but with the sound and noise i have now, i don't need a new fan anymore. I don't know why the Sunon fan cool better than the volcano at a much lower sound, but it works and i'm very happy... try this if you can't hear the reactor sound of your volcano fan anymore.

What's your case temp before and after you switched the fans? And what are the rated CFM for the volcano and Sunon fans?

My case temp is the same, 32C-34C The Sunon have 40 CFM and 33db The volcano 9 have 75CFM and 49db I know that the volcano have much better airflow, but the fact is that my temps are lower and the noise also...

The magic of case ventilation. I'd say the fast fan is drawing more hot air out of the case. Despite the "unchanged" system temp with which the sensor could be mounted at a spot unaffected.

real_cool: the fact is that i run the volcano at the same speed as the sunon, at 3000rpm, to have a good level of noise, so in theory the case ventilation have not changed..

Well, the amount of air removed by the fans are different even the fans are at same speed. Another possible scienario is that you bumped the heatsink during fan switching process and made the contact better between it and CPU. But if your heatsink sits very tightly, it's unlikely.

Athlon idle to full load temps hardly vary more than 10 C, dislike P4. If you had idle of 40C to full load of 58C, I could only conclude to your case temp had a lot to do with it. May be others could shed some light here. My XP1700+ at 2.18 Ghz idles 38C tops 47C.