My car is still under CPO and I have taken it in 3 times so far for the wastegate rattle. I actually went to two different dealers. The first time I went, Dealer A replaced the wastegate actuators. The second time Dealer A said they could not replicate. So I went to Dealer B and they replicated the rattle and replaced the actuators again.
At no time did they suggest or offer to replace the turbos. If the rattle comes back I go in again, I will bring up the turbo replacement.
'11 BMW 335i M-Sport Coupe xDrive [LeMans Blue] - COBB AP V3, BMS Intake, ER CP, Exotics Tuning CF Lip, CF Diffuser, M3 Spoiler, Eibach Springs/Bilstein Shocks
'07 BMW 335i Coupe & BMW Z4 3.0i