Noise can come from a number of places in an audio system. First solution, gain staging. Make sure you have correctly adjusted the in/out gains of each component in the system to maximize signal to noise ratio. EXAMPLE: You don't want to crank the output stage and have the input gain way too low. The result from this will be unwanted noise. Most units will have a "unity" setting for gain controls, which is the optimal setting for S/N ratio for that unit. Set your levels here, and when increased volume is needed, boost at the channel gain first. You usually want the channel stage to be boosted higher than the output stage for best clarity.
Second solution, cabling. You need to use good-quality cable (shielded if possible) that is of the correct impedance (low z or high z) for the application. When using unbalanced cables, you want to make sure that you keep your cable run as short as possible due to the fact that these cables send signal on the ground. This increases the noise (and decreases S/N ratio) the further the signal has to travel. For long cable runs 15' and longer, balanced cable is recommended. The shielding will keep unwanted interference (radio waves etc) from being induced into the signal path. This can also help cut unwanted noise.
Third solution, your electricity: When you are using multiple units with different ground connection paths, you can run into ground loops. There are ways to get through this, the simplest being the use of a direct box with a ground lift switch (such as the BEHRINGER DI100) or ground lift plug. This can kill the ground loop and the interference (noise) between the two conflicting units.
If you can narrow down your noise source to one of the aforementioned problem areas, you can make your life a lot easier. Give this trouble-shooting method a try, and if none of these methods helps your problem, contact our Customer CARE technical support team for additional troubleshooting tips, or if necessary, details on having your unit repaired.