Does the 320i have an engine cover?
I have seen this engine cover issue with a Mercedes Diesel, the cover came a little loose and the diesel rattle was more pronounced, when it was put back on properly, the engine sounded much better.
'05 E90 325i 6sp Man SG 118,032km on the odo (retired)
'06 E90 325i Step SG 121,021km on the odo (retired)
'08 E90 325i LCI Step | Space Grey | Black/Burr Walnut | Adaptive Xenons with HBA | CA | Navi Pro | 17in mixed tyres | 105,437 on the odo