What are Grounding Loops

Grounding Loops are a phenomenon we come across in signal cables.  The shield of the signal cables is intended to prevent interference from stray magnetic fields.  This shielding needs to be grounded at only one point.  

If the shielding is grounded at two points, there is a possibility that the two earth points may not really be at the same potential.  This can result in the flow of current through the shield.  This current which flows through the shield will create a magnetic field which can interfere with the signal cable.
Ground Loop
Grounding Loops can be prevented by ensuring that the shielding is grounded at only one end.  The other end should be taped and isolated.