My observations in point form:

At the very beginning, I get

1) lots of noise in shadows
2) Red streak (very bad, looks like rails)
3) Grain (or noise) in general
4) Even more noise if I crank up the brightness in Vuescan

In the first couple of days and I was so disappointed. But after some observations, I found out:

1) I get inconsistant results from the same slide
2) I occasionally get good scans even after I get a bad scans from the SAME slide

Then I realize:
1) If I do photoshop or something when scanning I get very crappy results
2) If I turn on the stereo I get even worst scans
3) I get good scans when I walk away from the room

So I have decided to:
1) When I scan, do something else except working on the PC
2) Turn off the screen saver
3) Turn off the auto launch of Photoshop in Vuescan if I am batch scanning
4) Place the scanner away from the monitor and speaker and put it on a very solid platform. It was originally 1ft and 2.5ft from the monitor and speaker respectively, sitting on top of my flatbed.

And you can see the result from:

http://www.photo.net/photodb/folder?folder_id=165504
http://www.photo.net/photodb/folder?folder_id=165505

They are all done in Vuescan 7.2.9, 4 passes, 2000 dpi, 72% Jpeg, dust removal, long exposure, brightness=1 (default), neutral color balance. Film were velvia and Provia something, some pushed 2 stops.

The result is pretty consistant even after 3 hours of usage. Personally I suspect the red streak issue is really an environmental issue.

Thanks for your help and comment,

Ken