There is now a simple way to fix the gauss sound distortion after loadings:
You must have it on 0 while playing. Putting it to 0 only in demo wont make a difference. And since you are playing on your own server, this cvar wont matter anyway.
cl_lw - This is called "client-side weapon firing prediction". What this refers to is the instantaneous set of effects that occur when the fire button is pressed. These effects are all done client-side if client-side weapon firing prediction is enabled (cl_lw is 1). The effects include: starting the weapon firing animation, showing any muzzle flash, creating any ejected shells, drawing decals and bullet puffs at the impact spot on the wall of the level, starting the weapon firing sound, etc. However, the actual determination of whether the shot (for hit-scan weapons at least) hit another player is now and always has been done at the server. If this is disabled, Lag Compensation is also disabled. (cl_lc)