Yea bud you shouldnt have to be dealing with this whatsoever. There giving you a bunch of B.S. in my honest opinion and having CPO warranty ALONG with the service bulletin for wastegate rattle for turbos should have you COMPLETELY covered, no questions asked. Especially since they already replaced your actuators and the rattle still persists. If I was you I would take it to another dealership and make sure you take ALL your mods off, just to be on the safe side since they are giving you a hard time for absolutely NO reason. And Envuks is right, wastegate rattle doesnt throw any codes or non that I have ever heard of.
If you still continue to have issues you might want to inform your attorney so maybe he can give them a call once he goes over the service bulletin and your CPO warranty...
A/W E92 335i M-sport with JB4 G5 ISO/ E40 WEDGE PERFORMANCE BACKEND FLASH, Alpina TCU flash for AT/Switch-tronic +AR Downpipes, Stett gen 1 intake, Wagner-Tuning FMIC+RB Turbo setup/ RB PCV Valve+ Akro exhaust+60% E85/93 mix,+ HRE P40S wheels, KW coilovers, M3 sways,+BMW performance CF Mirrors, BMW Performance CF deck lid spoiler,+ CF interior trim, p3 vent boost gauge,+ LUX angel eyes (11.73@119mph on street tires) NO METH!