Sound Problem

Hi there, for some reason when i start up garrys mod and join a server i notice the sound seems to be very low and quite compared to my settings in game and my system sounds of what i put my headphones too.

So when i join the server i have to go out of game, go to my sound mixer, and for some reason the bar for garrysmod is turned down to 6 instead of the original 50.

Please help if you can