Slow framerate for no reason

My game is set to 60fps V-Sync, I have about 300 objects in the layout and when running, it uses about 5% CPU. It usually stays on 60fps. However, occassionally, for no reason at all, it will drop to 45fps. CPU usage is still the same, no other processes are using the CPU/GPU, and a reboot doesn't help. It stays slow. Then randomly it will go fast again. When it was slow, I even removed ALL events from the layout and ran it, it went to 45fps after a few seconds and stayed there. This was last night. I did not shut down my PC overnight, and today, it's back to 60fps constant again. I'm quite puzzled by this behaviour since it isn't related to any events, and even at the default fps/timer settings, if it goes slow it will stay slow until it feels like going back to normal.

Any ideas?

What are your PC specs? It could have been background processes interfering. That's the good thing about computers - there's always a reason <img src="smileys/smiley1.gif" border="0" align="middle" />

It's an i5 with Radeon 6770 and 6GB of RAM. I looked at the background processes, CPU usage was under 10% (most of which was my game). GPU usage was also minimal. It's really weird, I can't figure it out.

That is really strange. How large are those objects you're using? If they are large texture sizes that might cause slowdown as the GPU swaps them in and out of memory.