[m1bjr]

There are codes and shadow codes.
Not all errors produce an idelible log in the 335i ECU.
Some O2 sensor errors cause a warning that is not logged but will appear on the dash until and engine restart.
I do find this car 'noisy' and have had a couple of odd random codes that never re-appear.

However...
Wastegates ARE a known issue on the 335i - there are two of course.
It's not unknown for (normally rear) actuator arms to require tightening or adjustment.
It's a pig of a job and expensive to sort though, so my guess is they are being lazy.
Many owners report wastegate rattle - slightly reving the engine causes a clatter, like a rattly exhaust, as the revs drop back to idle.
That's a turbo out job.

Steve