If the game freezes and you get a sound loop it could be low OS paged pool memory (not virtual memory).
I used to regularly enough have HL2, DoD and CS:S freeze with the sound looping and never knew why. Then I got TF2 and it was virtually unplayable cos it crapped out within a minute whereas the others were somewhat random.
Anyway after a bit of searching I found the problem was the Source engine can cause problems with the previously mentioned paged memory thing. I can't do much with the net at work but if this is the problem you're experiencing then run google search for low os paged pool memory. There is a registry edit you need to make and that may hopefully solve your prob (it did for me).