explorer starts ghost searches

Until last week I was quite happy with the Windows 7 explorer with the indexed search. On my 500GB data drive it finds anything I ask for, in over a million files, in a matter of seconds or less.

My C: drive is not indexed, I only install programs there and hardly ever have to search anything there. But yesterday and today I noticed something spooky:
While browsing C:/blabla/downloads (just 161 items) it is extremely slow, each time I click the scroll bar it starts with an empty window, then shows file names, then columns like date and size slowly get their information. While doing so the bread crump bar (or is it still called address bar?) turns slowly green, just like when it is actually searching something.

I haven't yet seen it in any other folder. BTW there are no hidden files other than desktop.ini. This is a few weeks old i7 with 4GB DDR3, the C: drive is SSD, so IMHO it's not strange that I expect more speed than Windows 3.1 on 4.77 MHz IBM PC-XT (yes, I'm that old, even older ;-)

My build number is 7600.16481. It came with my new computer. Event viewer shows nothing relevant. I decided to move all files from my
c:\ [administratorname]\downloads folder to drive M: because it was no fun browsing my downloads on C:. Each time I looked into a zip and went back to the folder listing, the slow green bar reappeared.
This morning I opened control panel>all control panel items and there was that awful slow green bar again... click on programs and features even took minutes to show all programs and icons.
This computer is still extremely fast compared to any other machine I've ever used for heavy math, 3d editing and rendering and such heavy tasks, but it's slower than some old Pentium 3's running Windows'98 when that green bar appears...
I already turned indexing on for c: shortly after I wrote the first message of this thread.