The Rotex, while versatile and powerful, isn't the smoothest Festool sander. As mentioned above, try turning the vacuum down to half or less. Its also critical to not tip the sander at all. Lastly, use the softest pad unless sanding edges.
The Rotex and CT22 were my first Festool purchases, and while I wouldn't part w/ them I finally broke down and got the ETS125 as it is soooooo much smoother and easier to handle. But its still hard to beat the Rotex when you need to remove alot of material.
Fred