However, if something was already loose, a thruster firing would cause the Shuttle to float away from it. Hopefully it was something small and in the bay. Something from the outside of the Shuttle would be bad news.
On the plus side, they can probably do a couple of small burns to get themselves closer to this thing, if necessary.
I don't know if they want to use up fuel chasing the thing down, especially if it's in a lower orbit. OTOH, it can't be too far below, since it's matching speed. Considerably lower, and it would be moving at a higher rate of speed.
Until they figure out if it came from the shuttle, which is likely, they would be in fuel conservation mode. They have to maintain attitude and continuously reposition the shuttle if they were to be required to stay in orbit for a extended period of time.
Right now, they are beginning the survey of the bay. I suspect they will also do a EVA tomorrow and reinspect the entire shuttle.
If they find a serious problem, they would have to re-dock with the station at some point.
I hope it is just a protective blanket from the bay.