Attac sound a bit weird

New with my TI2 but not wit older virus, I'm working with pad sounds with long attac time.

I noticed that I can hear a little snap sound when a note begins. I shouldn't here nothing ! The virus synth receives its midi notes via usb. Any advice ?

I noticed also that when I stop my daw, all sounds stop in the virus ! Even if there is a delay with long feedback ! It's surprising ! Does it cut any sound when the daw stops playing ? Can one avoid that ?
The little snap sound occurs either via usb or analog outputs.

Many thanks for help !

It seems I've found where it came from... (Finger cross !)
There was a sourround output in the utility section. I'm not sure it was the cause but for now, I don't hear any snap when a note starts.

Edit : it happens less often but it remains here.

But I still would like to know how to avoid the virus to cut sounds when stoping playback the daw !