Sennheiser's guide to running a frequency scan can be found here.  You should run a frequency scan whenever you move your XS system to a new location.

When the headset's cable touches the body pack's antenna, it can produce a clicking noise.  Here are the best ways to reduce or eliminate this:

• Try to create as much separation between the antenna and the cable by eliminating as much slack on the cable as possible (without restricting movement). Something like these velcro cable ties can help do the trick. 
• You may also consider using a lapel clip to keep the cable pinned to the instructor's shirt/athleticwear during the class to assist in the same way. 
• We have also received reports that using a bit of electrical tape on the cable, but not the antenna, can help improve shielding on the wire and prevent static noise. Simply wrap the cable with electrical tape a few times around where it connects to the body pack and extending up through the length of the wire next to the antenna.