Pulsing motors

[Hieb]

I'm hoping someone can give me an idea of where to start on troubleshooting a problem with our robot. It has just been in the last week that we've had the opportunity to test our code on the robot and after several failed attempts we finally have limited driving capability. Unfortunately the motors seem to be pulsing when the joystick is pushed to full. To isolate electrical problems we've pulled all the circuit breakers but 1 at a time and it occurs for each motor. To isolate programming issues we deployed a generic arcade drive program with no modifications and it still pulses. Any suggestions on where we could look next?

Thanks