I have a MacBook 2GHz with 1MB Ram. Never had fan noise problems until I did the upgrade from 10.4 to 10.5 (or so I thought). The software upgrade was frustrating because of the, now well known, administrator permissions glitches and an inability to complete permissions verifications. Since the upgrade and the really unbearable fan noise, iStat pro CPU A temps were in the mid 70's Celcius with Fan speeds in the 6000 rpm range. I called Apple and they agreed that the temps were too high and that I should bring the computer in for checking. The Apple Store promptly replaced a fan and the controller board and said that all was fixed. I brought the MacBook home and upgraded to 10.5.2 hoping that in addition to a fan noise fix, my permissions verification problem would be solved. Although there was some noticeable reduction in the speed at which the fan climbed to higher rpms (it then only reached an average of 5500 rpm with max temps in the 68-70 C range) it still was way too noisy to enjoy as a laptop (I've owned 3 mac laptops and none have ever screamed like this before). I went onto MacRumors forum to see what else I could find out about the subject but no one has really noted a solution to the problem. I tried using, Activity Monitor, Check Up....I tried avoiding Flash containing Safari pages, etc. BUT alas to no avail. As I wanted to print out one of the forum instructions on upgrading my hard drive, and since I was now at home where I don't normally print from my laptop (I have 3 different printer drivers loaded for 3 different printers at home and my office), I opened the Print & Fax Icon in the System Preferences Window to see if I had a set up for the printer at home and noticed that I indeed did have the driver for the Canon i860 home printer loaded, and there was a small note below the printer icon in the printer list stating that this printer was "in use" and set as the "default" printer. I found this strange because I print 99% of the time at the office on a Brother MFC printer that I thought was set to default. Alas, after clicking on the i860 printer icon, a dialogue box opened to state that there was a 2 month old, 2 page print job pending. I should note that there has not been a printer icon bouncing in my dock over the last 2 months and there have been no warnings coming onto my screen saying that I need to check the printer jobs, etc. BUT when I then connected my MacBook to the i860 at home, the print job processed and the Fan speed instantly declined to 1800 rpm with CPU A Temps of 45 C - PERRRRRFECT !!!! And it has not increased since then nor gotten hotter, nor noisier. FAN NOISE PROBLEM SOLVED.!!!!! I have since repeated the scenario ... that is, printing to a printer that is not connected to my MacBook and the fan immediately ramps up to 5500 to 6000 rpm with CPU A temps running at 67 - 70 C and if VERY noisy. I suggest those MacBook users with noisy fans should check if they have inadvertently sent a print job to a printer that they rarely use and if so print it on the correct printer or delete the job. They may get the same quiet success I have come to love once again. Hope this helps somebody else.