BMW 4.6 is poor acceleration and hesitation

[Aman]

Thanks for your reply
MAF is brand new but I will check the other things you mention
Any idea what the rattling noise from engine could be?
It's not there at idle or if you gently increase the revs, it starts to appear as the engine struggles at approx 4000 rpm which made me think is there any variable intake on this car? It's a 4.6is and I'm fairly new to x5s (this is my first one)
Occasionally he revs manage to reach 5000rpm without the rattle, but less often these days