Found this great article written by Rane Technical Staff in 1985:
- Cause and prevention of ground loops
- Interfacing balanced and unbalanced
- Proper pin connections and wiring
- Chassis ground vs. signal ground
- Ground lift switches
The article can be found here
A PDF version can be downloaded here
This article explains the cause of audio hum and possible way to prevent/ solve the problem. a must read for any audio people.