David, check this out:
The important excerpts from the bullitin, for those interested:
1) Run test plan.
2) The test plan will conclude with an instruction to replace the wastegate actuators; ignore this instruction. Reprogram the DME; improvements are included with the following I-Levels:
E90, E92, and E93 (335i and 335xi), E89x-08-03-530 or higher
3) After programming is completed, if the noise is no longer present, take no further action. If the noise is still present, replace both of the turbocharger wastegate actuators in accordance with Repair Instruction RA 11 65 580, Replacing vacuum unit (wastegate) (N54).