Why do I have random lag spikes when playing GMod on my TV? (Laptop hooked up to TV via HDMI)

Like, I would be having solid smooth 60 fps, then every 10 seconds it drops to 30 then back up to 60.

My tv is 32 inches, and the resolution is set to 1280x720 when i hook it up.

Laptop Specs:

GPU: AMD Radeon 6650M 2GB Vram
CPU: Intel Core i7 2630QM Quad Core
OP: Windows 7 Home Premium 64 bit
Resolution: 1600x900 (1280x720 when i hook it up to the TV)

When I play Gmod when its not hooked up to the TV, it stays at a solid 60 fps with no lag spikes or drops.

this happens with a lot of games when you hook up a computer to the tv. it’s not just a gmod problem.

Why does it happen, and is there any way to solve this?

Ever since the recent updates the game has been laggy as hell

My old MSI does this too. Yet I haven’t got any idea what causes this.