I'd say just take more liberty with the line. Something like
"Rumbling/clattering in the distance, the Ballistae start/begin to approach."
I don't know what sort of character limits you have to deal with though. If that's too long, maybe just get rid of the comma.
"The rumbling/clattering Ballistae start/begin to approach."
Whichever combination sounds best. To me "While creating noise," just doesn't really sound like something someone would naturally say, and "noise" just isn't very descriptive of a word.
(My brain is in high school proof-reading mode now, I am sorry. lol)