SONAR X3Producer - Big Drop outs during playback and Recording

Hi,
 
Over recent months I've suffered from big audio issues, having worked on changing many of the settings I'm at a loss how to solve, I've changed buffer sizes playback and recording (512, 1024 etc) and most of the other suggestions that are recommended etc. What happens is that playback stutters etc when I'm working within Sonar and other apps. I only need to click on explorer for it to suffer.
 
I'm using 64 bit W7, i7 2.67 GHz with 12GB RAM, ASIO drivers I have a M-Audio Fast Track Ultra sound card (changed these settings too)
 
I'm seeing peaks of 35% in the CPU monitor when this happens, it happens also when I'm not doing anything other than playback also.
 
Any advice, it seems to be a new issue as it was once quite stable
Thanks
Matt
 

Since this started in recent months, the obvious question is, what changes were made to your system in that time?  Anything new installed?  A recent program update may have installed something now running in the background.
 
- Go to Control Panel, Programs, and sort by Install date.  Look at the software recently installed.  See if any are conflicting with your DAW operations. 
 
- Check startup (msconfig) and if you don't recognize something, disable it.  (Any of these changes are easily undo-able).
 
- Any chance you're getting to the last 10% of space on your C: drive/partition?  This can cause problems.
 
- Run LatencyMon (free utility).  It'll report any problem areas latency-wise.
 
- If you know how to look in the event viewer, do so.  Any recurring system errors?
 
(I've purposely left off checking system settings for now since you say the problems are a recent development, and unless you did a OS reinstall, these settings can go farther down the list).