FPS Drops

Hey! Since last thursday, I've noticed an issue: After about 4-5 minutes playing beamng, sometimes (Not always) my FPS fall severously. For example, I'm playing gridmap with 40 FPS, and I don't know why, FPS fall to 3-4. It doesn't matter which map I'm playing in. Even Running the game in safe mod or deleting the mods doesn't work... What's the problem?
Cheers and thanks