This cart has gone through a season with non powered mecanums. They do make some noise, but they are not loud at all. If anything, they make people turn around and realize that there is a robot behind them.
Keep in mind this was tested on tile floors with decent grout gaps.
And to Nate: This was our prior cart.
http://www.chiefdelphi.com/forums/at...5&d=1333563144
http://www.chiefdelphi.com/forums/at...6&d=1333563152
V-belts are a good option. We don't know if the belts would slip under the stress though.