Main weapon keeps switching to gear slot four

Had this problem on and off four a long time now.
I will happily be playing the game when suddenly my rifle/Carbine will switch to gear slot four. It can happen during a reload when i fire one shot with my gun sometimes just when am running around. The game becomes un playable as the rifle will switch to C4 triggers a mine or resto kit depending upon my class the only way to continue playing is to get in a vehicle. When it happens it will continue to swap to gear slot four no matter how often i press button 1 to re equip my rifle anyone watching must think am juggling.
I have changed out my keyboard mouse and updated my files but it keeps coming back. I have raised a support ticket but for some reason they are not responding. Anyone else had a similar problem to this?

I think I remember have a similar issue a while back, and it was my mouse. But that worked for me.

Try binding equipment slot 4 to something else and see what happens.

Thanks for you reply's but i have already tried those options and as i said i have even replaced both my mouse and keyboard