Steam Overlay causing framerate drops?

[Mallikeet]

I've noticed that whenever I have the Steam Overlay enabled, Steam will go up to 8% CPU usage at random times, usually for about 3-5 seconds, and during those times CSGO's framerate will seem to cap to about 45-55 FPS, though the actual ingame FPS feels about ~20. This will typically happen every 2-3 minutes.

Disabling Steam Overlay removes this random drop, though FPS still drops sharply during firefights.

Anyone else experienced this?