Thanks Sensei!

Well I took my Graphics card to a PC shop and asked a technician! there if he could dismount my GPU Heatsink and clean the heatpipes. He said no, he has no experience with Graphics cards but he took an airblower and blowed through my card and demanded 5€ for that....

back home I got thermal compound and wanted to dismount the heatsink myself, I removed all the screws but the heatsink was like superglued so I left it as it was. Then I started operation Dust Buster. I took my vacuum cleaner, set it to 1600w and then tried to clean as much dust as possible out of my PC. For the CPU fan I took a brush which got a few dustballs out.

Anyways I sticked the Graphics card in and was shivering like hell, my hand shook that much that I almost was unable to place the GPU slot screw back in.... Ok I turned the power on and heard a shhhesssh like sound for a second then my PC went back to almost silence.... it got a tiiiny but louder as Vista was booted.... anyways, checked Everest, GPU back at normalish 80°C idle and CPU at 46°C idle :D

Started Sims 3.... PC got loud but no where near vacuum cleaner level.... I was able to create a Sim without thinking my PC will blow up any second... :D

I seriously hope it stays that way..... I have the impression that my PC runs much quieter although in some seconds I think I hear my PC in its old state... I think I got a bit Audio Paranoid xD

One question remains open... double you tee eff happened to my heatwaves? When my PC got hot I always got heatwaves in my face... annoying but I was atleast sure that the heat goes out....