FPS alternate each time I run my application. Sometimes it's 100, sometimes its 500...

I've got no explanation for this.

Every time I run the game inside the Unity editor, the FPS will either stay around 100fps or 500fps, but It seems to be randomly decided, as I can't find a reason for the alternation.

I've checked every start function to see if any random numbers are generated at the start of the game which may be responsible for the variation but I didn't find anything.

Thoughts?