pulsing motors

[tilky]

i wrote a program in labview, starting out simple, with a tank drive in 2 joysticks and arcade in a 3rd. The code worked fine, however, with troubleshooting tehniques, we narrowed it down to the program. When we loaded the program into the robot, the motor made "grinding" noises, but only when we ran it off of the code (when we connected it directly to the battery it didn't do it). What it seems like is happening is it runs the motor, and turns the motor off hundreds of times a second. Has anyone ever heard of this problem happening and how to make it work?