Hey,

Filters are probably your first and last line of defense against jittery data.

As long as you have plotted curves, open up the filter tab, and in the f-curves window select up a range (or the whole range if you have to) and try Butterworth or Smooth… Peak Removal or even Key Reducing sometimes can help too… but the former are your best of bets.

If you haven’t ever done it before, a tip ‘cause it’s strange, you have to preview and then hit accept to apply the filter.  I don’t think you can just hit accept.... 

You have to play with the values too, see what suits your needs.

And if that doesn’t work, maybe look into however you made the .bvh and smooth your data before it comes into Motionbuilder.

Best of luck