Certainly no difference with noise.....I never heard wetside noise anyway. All the noise for me comes from the dry side. Of the four 2006 MP40's I have, I had to buy new QD wetsides for three of them....magnets swelled up. The three differences I noticed are:
1. No longer can you take it completely apart down to the ceramic bearing. QD drive is similar to the MP10 wetside where the impeller and back plate stay together.
2. The cage on QD is open all the way around. The old cages had a portion of solid plastic.
3. The space between the cage bars is slightly larger with the QD.