You noted that many web pages do that. It's the scripts on the page or even animations.
Nothing busted here.
My pc has Win XP(Sp3) and IE 7.0. When I open a web page my cpu usage(task manager) in iexplore.exe runs at 80-85%. Obviously my pc becomes very slow. I use Symantec Endpoint Protection and perform weekly scans. I have also performed other malware scans. I might add this does not occur in all web sites but in a large percentage. The cpu usage will remain high for awhile and drop to normal and then spike up again.
Any suggestions as to what might be causing this problem?