I'm loving the A310 for MSFS right now, its an awesome plane and all but theres one thing that I think should be much improved and looked upon more, the engine sounds.
The idle thrust sound is way too low and going from idle to 50% sounds like starting your engines rather than spooling the engines for takeoff and the iconic whine of the CF6 is missing (look on youtube for references).
If the current engine sounds can be improved upon, that would be great! 
 

How can I turn off the sound in background? I still can hear the plane when looking at other program.

The in cockpit sounds are hideously loud. I have the sound options in MSFS set to 1 (on a scale of 1 to  100). Still the noise in way too loud. Of all the many default and addon planes, over 50, not one of them sound even 10% this loud. I don't understand how the developers released it like this. It's not just me, Avsim forum people are complaining of in cockpit sounds too loud.

We recorded the plane IRL - it is indeed very loud in the cockpit. 

We have recorded a lot of feedback, and team will work on this now. 

Will ensure these feedback points are addressed and in the next version.