I can confirm that the settings change did not fix the problem, as it happened again just now. Only thing I've changed since was enabling antialiasing.

I returned the sound channels/sources setting to 64 and the issue seems to have gone, as well as the random zombie and can noises, although it may also be the server, as I've noticed this happened more on vilayer servers.

I found that if I was putting the ammo or first aid boxes on the floor it would take 20 seconds to appear each time, seems consistent. I put them into hands now as it's faster, though you can only see the first 6 slots.