Lost Bus/environment Sound

For some strange reason, the sound of the bus has gone as well as other road traffic.

I can still hear the passengers when they enter the bus, but every other sound has gone.

Suggestions?

It should come back after a few minutes. I had that a few times, thought i would have to close my game, but it tunes itself back in after a bit of driving..

Alright will keep at it, on my 7th tour and coming to the end of the shift.... really annoying lol .. ta