Hi Keith,
A couple of things. The reason that their is ripple on the 0-10V control signal is most probably due to ripple on the power supply feeding the 0-10V control circuity. Less ripple should produce a more stable signal.
More importantly, it sounds like the acceleration parameter the VFD is too hi. If you reduce the acceleration parameter, the speed fluxuations should be smoothed out and a steady peed should be the result.
Cheers,
Peter.