In virtually every television environment audio hum can be a problem, either in a studio or out in the field. Even digital audio becomes analog eventually.
Solid system design work can make the instances of hum minimal, but it will show up eventually.
The most common causes of audio hum include unbalanced cabling, long cable runs, audio equipment connected between venues with separate electrical panels or services, poor electrical wiring, or interference from other equipment. Sometimes, the cause is never known, you just want it to go away.
Whether you are in the field or in the studio, the solutions are typically the same. First, make sure that the hum is not just in your monitoring circuit. It would still need to be cleared, but your product would not be suffering.
Next, check all of the connectors for proper pin-out and integrity. This task is made much easier if you use connectors that come apart quickly and without tools.
Try to consolidate your electrical connections to as few different receptacles as possible (while taking care to not overload circuits). Don’t be afraid to use extension cords to accomplish this. Often, using a three-prong to two-prong AC adaptor will alleviate hum. However, proper care must be taken with regard to safety.
Finally, when wiring balanced audio, it is a common practice to leave the shield disconnected at the signal destination. Don’t be afraid to “lift the ground” to see if this helps.
