Yeah this happens quite often during heavy encounters, be they ground combat or space battles. Once the effects start to drop out, the only way to fix it is to relaunch the client. I've tried tweaking sounds in different places, but no luck so far.
Sometimes it's not too bad, but often it sounds like listening to the fight from a distance down a corridor. Kind of a surreal feeling at times, but as it's not intended..hopefully the issue can be identified and nailed down soon.