rear-ended while parked--what to look for

My parked Honda '05 Coupe got rear-ended while parked and it shifted
forward 3-4 feet into the back of another car. My car drove home fine,
but the next day, it started making a squealing/hissing sound in the
front. The sound only happened when it was in drive, reverse or
neutral. Do you know what that could be? I took it to the autobody
and they said it was probably something related to fluid in the brakes
since it rained the day before. I thought it was more related to
getting rear-ended and told them that. They said they'd check it out,
and now, 3 days later, the autotechs say the noise is gone. Do you
think the transmission could be damaged? I had my parking brake up to
when it was parked.