Bad Company 2 Sound problems

Oh, well, HELLO everybody. I have a little problem with Bad Comapny 2 (and newer Battlefields) that i can´t hear some of the voices in the game. Game runs perfectly at 60 fps somethimes it drops, but not that bad. I just play and start to shoot and reload (nothing) , and when tank hits a wall i can't hear it as a soldier. Somethimes i have ECHO problems.

It happened worse in BF3. I had no problem with crysis 2 or Deus Ex.

Specs.

Core 2 Quad q6600 

4GB Ram (zeppelin 1x800mhz and 1x1333 mhz)

Motherboard Intel D946gzis

Graphic: Nvidia Geforce gt 140 512mb, 57gb memory brandwitch ... (upgrade soon)