Congrats on your Levante! Gladly, I have few solutions which should help you regarding these problems.
As to the exhaust, it seems that the exhaust valves or actuators might be to blame. If it cannot be found it most likely is acted upon by an actuator possibly somewhere near the exhaust manifolds. In addition, it’s important, I think, to inspect the wires and fuse connections for the exhaust valve as well. If that is all okay, you may wish to have the actuator tested or even changed.
For the leaks, sounds like it could be coming from a few: First ensure door welts and sun roof drain if any are not credible. The problem with the front window might be also connected with a blockage of the drain channel. As for the rear footwell it can be due to a blocked drain or a weeping door skin. Regarding the boot, well you said that the adblue cap was off so you need to check whether all the seals and covers are secure. Often it helps simply to re-seal and clear those channels which had become blocked in some way or another.