Sabertooth 2x32 and SyRen25 interfering with arduino

So Im building a large scale remote control tractor trailer. Im using the Sabertooth 2x32 to drive the dual drive motors and the SyRen25 to control the steering servo. These drivers are controlled by the pwm signal from the rc receiver and not the Arduino. The Arduino controls my lights, horns, switches for the radio ect… I do not have a problem with my code… as far as I know. Im picking up both signal wires off the 2x32, throttle signal and polarity reverse signal. The throttle signal controls my break lights, and the polarity reverse actives my relay to turn on the back up beeper and lights. Other than those 2 wires, nothing connects the drivers and the arduino together. Now, when I have power going to everything, NO MOTORS WIRED TO DRIVERS, everything works flawlessly. As soon as I connect 1 of the 6 motor leads, does not matter what motor or what lead (2 wires per motor, 2 drive motors, 1 steering motor) the Arduino starts going nuts. Relays bounce on and off, my sound card goes crazy and Im not touching a switch on the rc transmitter. Even hooking a multi-meter lead to one of the driver outputs sets off the Arduino. Now Ive tried just about everything I can think of, from changing where everything gets power and grounds, to trying different motor drivers, to adjusting my code. Anyone have any ideas??? T.I.A.

Sorry I do not have the time to chase down all the parts and find the needed technical details then create a schematic so I can see what you did. Of course I can plainly see the code and maybe around the 40th line there may be a problem. If you post the code and a schematic, not a frizzy thing and links to giving technical information on the hardware parts you will get a much better answer. Remember we are not at your side looking at this.