When you notice that your CPU spikes to 100% what are you doing with it? A little more information would be great.
If you look at my screenshot:
You can see what programs are using what amount of the CPU. In your case when your CPU spikes to 100% which application is using the most. (When in Task Manager click CPU twice to put them in descending order.)
If you do not have a column heading for CPU then do this:
1) Open Task Manager
2) Processes Tab
3) View
4) Select Columns
5) Check CPU Usage and hit ok