If it was me I'd try from the engine bay identify where the rattling is coming from, I believe your timing chain is on the rear? The EGR is front right if the same as the M57 (by front I mean headlights, and rear windshield) it doesn't sound as smooth and metallic as I was expecting to hear though. But given the chain is at the rear that may be a quick way to rule out chain.

Just seen the codes as well, it's worth having a look at the EGR, again if the same as the M57 just pop the hose off the throttle body and take a look down the EGR with engine running, if the EGR valve is stuck open you'll see exhaust gasses that would explain the hunting idle as it would constantly be fed exhaust gasses.

Another update, the hissing noise on LHS of engine, does the EGR on the N57 operate via vacuum? If so there may be a vacuum line split as the vacuum starts from the brake vacuum pump then under the intake manifold you have T lines to go to the engine mounts, EGR, Turbo. Swirl flaps and the main hose continues to brake booster.