So I noticed performance on youtube was stuttering at best and even Pandora seemed to be having issues. I thought it might be Firefox 3.6.16 but I run the same at work with no issues on an machine that is approximately the same software load, etc. And if you’re wondering why I haven’t upgraded to Firefox 4 yet, it’s because it breaks a ton of Java apps.
So I did some digging, brought up the task manager and sorted by CPU time. I noticed a process, MsMpEng.exe kept sucking 80% to 95% of CPU time. That would definitely cause stuttering video and audio.
So I killed the task and lo and behold YouTube and Pandora played nicely. Downloaded a fresh copy of Windows Defender (Last time I did that was 2007!). Installed it and now all is well. If you’re curious they really haven’t updated Defender app itself in a long time. But removing and re-installing it did the trick.