For filtering Ricochet servers I'd try a program called The All-Seeing Eye which you can get from www.udpsoft.com. Fast, resourseless, and free, it's my favorite:)
As for the sound problem. Press escape and then minimize from the HL menu. Usually this works. If not, pressing Alt+tab+ctrl+shift (one of the keys is not needed, not sure which) when leaving and entering the game will bring it back. If it does not come back, repeatidly use those keys, and it will usually come back. (yes I know, it sounds absurd, but try it)
As for the sound problem. Press escape and then minimize from the HL menu. Usually this works. If not, pressing Alt+tab+ctrl+shift (one of the keys is not needed, not sure which) when leaving and entering the game will bring it back. If it does not come back, repeatidly use those keys, and it will usually come back. (yes I know, it sounds absurd, but try it)