If you have a Moonroof (a glass sunroof) which sits too low or too high it can be adjusted reasonably easily. This can reduce wind-noise if the Moonroof was far out of alignment, although wind-noise is normally due to the windscreen trim rather than the Moonroof.

The correct alignment (Moonroof only, sunroof's are different) is:
Rear = level - 1mm higher
Front = level - 1mm lower

Use a Torx screwdriver with a rubber handle - danger of breaking the glass
Loosening the adjustment screws too far might mean that the rear of the Moonroof gets caught on the aperture when it tries to move backwards. This can damage the mechanism although the current-limit should stop this happening.

How to adjust the Moonroof:

Inch the Moonroof open by poking the switch upwards until the Moonroof is fully raised....go too far and the Moonroof will close and slide backwards. The adjusting screws are hidden behind a pair of rubber bellows, the top of these need to be pulled away from the Moonroof to gain access. They are attached to the Moonroof using a long tang, the bellows have an extrusion which pushes onto the tang. Here's the long tang:

So, start by pulling the bellows at the top fold, right in the middle of the bellows, the rubber will only move 1mm or so, do this all along the length of the bellows working backwards and forwards, eventually the bellows will pop off the long tang:

There are six screws that secure the Moonroof in place, these need to be loosened slightly (they are pretty tight to start with), two at the back and one at the front on each side. It is difficult to see the front screws (and impossible to photograph them)!:

Front screw:

Back screws:

The best plan is to loosen them very slightly to start with as if they are too loose the mechanism may jam. Close the Moonroof and then put pressure on the glass in the direction it needs to go. Raise and lower the Moonroof and check that it settles in the right place. A certain amount of fiddling is required to get the exact position and it is possible that you may have to loosen the screws further, however it is much better to start with them too tight to start with.

Once you are happy with the level re-tighten all of the screws and re-check the level. If all is OK push the bellows back on the long tang:

All done....Time for a cup of tea!