Interupted isn't the same as inaudible.
It's a toughie though. With interview transcripts they'd just put an
in place of the part that's inaudible.
This is how I think it would go in a screenplay.
Let's say the full sentence is this and the
BOLD text is what you want to be inaudible:
Johny are going to the museum to see the dinosaur exhibit."
I think this is how you'd make parts of it inaudible.
(INAUDIBLE) are going to the (INAUDIBLE) to see the (INAUDIBLE).
That's just me guessing though. The best bet would be to find a movie that has a similar scene,
then find that script and see how hat writer did it.