As per subject title and as you already know, there is recorded dummy conversation heard between time ATC gaps.
This is a long time heritage since FS8 era and continues still today with P3Dv5.
So, I wonder if you could do something to eliminate it, as it is annoying especially during long flights.
There is a gvp decompiler here: http://mormegil.wz.cz/flying/gvpdeco/gvpdeco_en.htm
You will find the background audio loop I mentioned in the gvp file – it might be the same played at full volume in your case, I never paid much attention to what was in that audio track.
Besides that I do not recall finding anything similar inside the file – but there are thousands of files and I am always processing in bulk so I might have missed it.
I do not thing people doing for example ATC tutorials on YouTube would edit out the sound, so I think it is not present on all systems. There are not many settings on the user interface, but there might be a pesky in file setting somewhere – but I would not know where.