I recently did the MKIII clamps (Previously wasn't using bolts through the metal cage) and my 360 has been working fine, but recently noticed the voltage on the fans will climb very quickly as soon as it is started and keep getting louder and louder until they max out and stay that way. This will happen with any game, even just idling with a game running.
The temps blowing out of the back are under 100F and I can have the box open and completely remove the fans and the unit will keep running just fine for 10+ minutes on heatsinks alone, so I'm not thinking it is an overheating issue (temps stay within range on the heatsinks and board). I had been having problems where the GPU fan would no longer work, so I had wired both fans to the CPU plug and that had been working just fine. Today I decided to check the GPU plug again and it was back to working, so I connected things like normal again.
The heatsinks are making perfect contact on the dies, but I'm not sure if something perhaps is messed up in the fan speed department or maybe some other issue I'm overlooking? Too tight on the bolts maybe? Things had been working fine for years with low temps and low noise.