Spiking CPU Usage in Windows 7

So I've noticed that while having only Excel 2013 running in Windows 7 on my Mac causes the CPU usage in task manager to spike up to 90-100%. It doesn't stay there for long (a few seconds), before falling back to say 2-12% (for a few more seconds), but then it goes back up.

I'm running Parallel 9 on my MacBook Pro Retina, so I don't think it's something wrong with an outdated CPU or something.

Is there anything I can do to resolve this?

All settings are default Parallel 9 settings.

EDIT: I tried changing optimization settings, to give Parallel 4 CPU cores, and 4GB of memory, and though now the task manager shows CPU usage of like 1-3%, Excel is still lagging.