Chat with him really quickly and he said LIGHT tapping is normal, which coincide with BMW claim especially when the car is started cold. He added even the 330i, 335i, X3have these weird hydraulic lifters noise, but they should go away after break in, some lingers on but that doesn't seemed to bother some owners.
He cannot assume anything on your 320si (N45??) since that model is not sold here and he can only assume that if the software upgrade is done, wiring harness checks out fine, and no error codes is registered, get them to replace the engine if the problem persists. Does the car has Valvetronic? You are not using any oil based air filter like K&N right? I had that happened once on my mk3 VW vr6, messed up the potentiometer inside the MAF, causing irratic idle and I got the MAF replaced under warranty anyway. Tossed the K&N and got ITG instead.
Anyway, your problems sounded pretty serious for a car that new. Keep me posted if the cause is identified.
