To branch off what BMWN54tech mentioned, I literally just went through this over the past 4 days.
Brought my car in because I had an oil leak (not related), but also noticed some lower coolant levels, excessive white exhaust, slight turbo siren at low RPM's, and some mild wastegate rattle upon deceleration.
Told the tech about the abnormal turbo noises, and also mentioned the wastegate rattle. Tech noted that the turbos sounded normal, but heard the wastegate rattle and changed 1 of the turbos immediately, no questions asked. Also helped that I mentioned that 1 of the turbos had been replaced at 30k miles due to wastegate rattle.
Moral of the story, doesn't hurt to mention these other symptoms if you're already planning on bringing it in. (and it seems like the rattle is a more justified reason for them to replace turbos. Also helped that the shaft play was out of spec..)