Vista - High Explorer CPU utilization

Hi everyone

I have a strange problem with the explorer. Whenever I click Computer or press Win-E, CPU utilization on two cores of my Q6600 shoots up to 50-60% leading to the fans spinning up and the machine not going into standby. Task Manager shows 25-30% utilization on explorer.exe, but there's no audible disk activity.

The CPU utilization doesn't go back down until I browse into any subfolder i.e. C:\Windows or D:\New Folder, it remains high as long as I browse Computer, C:\, D:\ or any other root drive. Once I've browsed into a subfolder, it also doesn't go back up - even if I browse back to C:\ - until I open a new explorer window.

Now for the strange part: If I start explorer by opening explorer.exe directly (for example with a shortcut to %SystemRoot%\explorer.exe /e,C:\ ) this doesn't happen. It also doesn't happen if I boot in safe mode, but deactivating all services and startup programs in msconfig doesn't help.

So can anyone tell me what's different about opening explorer.exe by clicking on Computer on the desktop or by clicking on the file itself
And of course, if anyone knows how I can stop the cpu utilization from going up, I'll gladly hear that as well.