(ET) Motor weak and pulsing (Alltrax)

[Steve Gaarder <gaarder ecovillage ithaca ny us>]

I have an E-15 with an Alltrax controller and BB-600 batteries.  All of a 
sudden the motor has become very weak and its output pulsates like the 
sound of a wheel with a flat spot.  It does this even in neutral, and when 
it's in gear it draws a lot of current (the current varies in the same 
rhythm).  Also the motor is quite hot.  Any ideas?

thanks,

Steve Gaarder