I have just gotten both turbos replaced in my 2008 n54 135i - under CPO coverage (ends April 2014). Thought I'd share my experience with you good folks and return back to this community.
I have had the rattle for around ~1 year now and it definately gets worse as time goes by.* At first I just ignored it as the car runs fine for everyday use (I only drive hard once in a while, here and there), no time from my work hours, and I usually listen to music when I'm driving.* Driving in and around parking lots, especially underground ones were pretty embarassing though as people who turn to see what car was making such noise.*
I've been a lurker on this forum and have read many threads/posts about the rattle and getting the dealership to fix it - sounds like they usually give us Canadians a hard time about it!
The replacement process all started when my waterpump failed.* While the car was getting repaired at the dealership (fully covered by CPO - no questions asked), I also brought to their attention about the rattle.* The SA's initial assumption was "a loose heatshield", and that I will have to pay $135+tax for diagnostic fee.* I did not have time to address the rattling issue and argue with them at the moment in time, so I just told him to document it and I will be back again when I had the time.*
A month later, I went back to the dealership on my day off and told them to look into the rattling sound (I was pretty darn sure it was wastegate rattling from the hundreds of threads and postings I have been reading / researching on here).* The SA arranged for a shop foreman to go for a test drive with me.* After the test drive, the foreman thinks that it had something to do with my exhaust (beating around the bush?* or perhaps they have to go through all these diagnostic procedures before they could officially request from BMW NA on performing a big warranty job such as replacing turbos).* During this time, I really wanted to tell them to stop wasting my time and that it was wastegate issues, but I decided it was a smarter move to play it "dumb" and "cooperate".* They kept my car for another entire day and performed a "scope test" and "intake and exhaust system leak check with the smoke machine".* No air leaks were found.*
I recieved a call from them the end of that day, and the SA says that there were no issues with my exhaust.* Next step is to drop my turbos, and "go on straight time to perform benchmark test as per DIS" to get some values and send to BMW NA to see if the turbos were out of sync to the point where they would approve new turbos.* This took two full days.* I recieved another call in the morning of the third day saying BMW NA has approved of new turbos and they will be replacing mine (takes another full day).*
All in all, although the process was pretty tedious and time consuming, it was all worth it!* I am a strong supporter of CPO.* Out of it, I have had new weatherstrippings replaced, new radio, exhaust checked for free, and new turbos.*
The best part?* I only paid $50+tax deductible for all of this (all $135+tax diagnostic fees refunded after they have confirmed the part was covered)*
I'm at work at the moment, but will scan the invoice for you guys when I find the time
PS-* A little friendly pointer:* Don't go into the dealership thinking you know it all.* Be courteous, cooperative, but also let them know you know what you are doing.** I think that helps when asking for a big "favor" from them.*