Engine sounds silent after using reverse

Engines sounds are normal through flight. On landing I select reverse (F2) then deselect (F1). At this point I lose engine sound. All I get is ground rumble and environmental sound. Spooling up to full power there is no sound, just more rumble as speed changes. Engines are working and develop power. My spec:Core i5 @ 4.6ghz4mb ram120gb ssdGtx 460FSX sp2 accelRex2 overdriveEzdok