ASP.NET High CPU Bringing Servers to their Knees

I suggest doing memory dumps and analyzing them in WinDdg with Sos. I fixed some problems on our production I probably wouldn't be able to diagnose without WinDbg.

Tess Fernandez has great blog where you can learn how to analyze memory dumps.

This is typically caused by large long-lived object cleanup in the GC(stackoverflow had this problem, see link). Are you storing lots of object collections in cache or session?

Assault by GC

I also recommend you build and configure a new server in production to test. If you have random craziness and don't know why and can't reproduce it, I'd point the finger to hardware or configuration, not code.

Is this a virtual server with shared resources or a physical server? If it is the former perhaps you could look at dedicating resources to this server. Good luck...