Assuming you're not trolling, all turbos whistle as part of their operation and if you push them really hard then you'll add in the chirping from the wastegate venting excess gas... :wink:
Might be different on more modern turbos but certainly in the old days you had to leave the engine idling for 20 seconds or so after stopping from a hard blat otherwise the turbo bearings 'could' be damaged from lack of oil cooling as they're generally on top of the engine.
If you're in the habit of hard revving a cold engine then that's not going to help either.
