[N5GKP]

It's hard to tell from the video as sometimes they can make it sound a lot louder than it actually is. The N53 injectors are quite clicky when the engines running anyway - most are that I work on including my own.
If you're buying from a dealer/trader I'd be inclined to make sure you've got a warranty that covers everything (up to and including injectors, high pressure fuel pump, etc), then get it booked in at BMW or a specialist for a check over