TT whistling after car shut down

alanforn

On normal start up driving home from work car shuts down quietly. Lately when I get home I shut the car down go into house to disarm house alarm, open the garage door restart the car, pull it in and shutdown. When I do this after turning car off there is A high pitched whine sound from exhaust that continues for a few seconds then winds down, literally sounds like the turbo is still spinning until depressurized. So basically this happens as quick as I start, pull in garage then shutdown so cars probably running for 30 seconds or so. I could always just keep the car running when I get home but wonder if this is normal or is something sticking (BOV)? Today I let the car cool down for an hour or so then pulled into garage, same thing happens.
??????