My first 60gb PS3 developed that soft whirr and it evolved into a big whirr, think playing card in bicycle spokes from when we were kids.
So now this 80gb MGS4 one is on the same soft whirr path, and hopefully wont evolve into the loud whirr.
The whirr is the fan bearings getting clogged with stuff. Same thing happened with my PC fan, but that one I was able to take out, disassemble, clean and reassemble myself. The PS3 not so much, especially if its under warranty. It it was out of warranty, I would not hesitate to try before spending 150 dollars on a repair.
I wonder if they would repair an out of warranty PS3 with the seal broken for the same 150 dollar fee...