Random thoughts: technically while shadow-jumping your both in the prime and in the shadow-plane, in kind of liminal state. So technically the speed your travelling, if the prime loosely fits RL physics, would break the sound barrier...

I think a woosh is preferable to...
Fox carefully sneaks into the Fort, tip-toeing past the guards. she lingers in the shadow around the outer walls before spotting an open window on the ground floor, "perfect" a sly grin crosses her face. *SONICBOOM!* "oh crap!".
ermmm yea...