At long last and searching for the right car at the right money, I have purchased a 535d M Sport - and clearly evidence shows they are brilliant and fabulous.
However, I need to ask some questions!
I have noticed on hard acceleration engaging both turbos will inevitably (and oddly?!) sound like you have just caused a hole in the exhaust underneath the driver - sounds like a Ford Transit, and is VERY noticeable. Leave the car go cold or drive sensibly for 15 miles or so, the loud exhaust sound goes away like a switch and reverts to the refined noise and at speed with no Transit noise at all, like you experienced when you bought the car. I have changed the vacuum hoses with silicone, now both turbo's engage perfectly, unlike with the original BMW rubber hoses - which are a complete waste of time.
Secondly - Under rapid acceleration the gearbox forgets to engage one of the higher gears, (possibly 4th or 5th) the revs go up on their own slightly then the gear engages with an almighty bang as the gear goes in....it is not a pleasant experience - and I have started to feather the throttle at this particular point in acceleration to avert this lack of drive in upshifting. Any ideas what is wrong?
Lastly, a pizzle of exhaust (?) smoke has decided to emit from the breather at the rear left of the engine, (as the car faces you), and I have ordered another. The smoke comes from 3 or 4 areas from around the seal, sadly. Is the car safe to drive whilst the new one arrives?
Any advice on these problems is greatly received!!