Only time I went on the McD was when Airtours were using them back in the late eigties early nineties.
Went MAN to the Canaries and got parked in the last row of seats. The loudest most uncomfortable trip I have ever had, and it gave me one of the worst headaches of my life.
On the way back I got in about row 6 or 7 and it was a great ride, smooth and quiet.
Seems to tie up with everyone else's experience.