DISTORTION AND INTERFERENCE

Distortion and interference can result from several different causes. Check the essentials first: Make sure the mic has a fresh, fully charged battery. If you have a lavalier and a hand-held mic for the some receiver, be certain only one of them is turned on.
If you use more than one wireless system and they interfere with one another, relocating the receivers may help.
Some external RF interference may be beyond your control, especially in an urban area. If this is the case, try to determine which wireless system is being affected. You may have to send the system to the manufacture to have the frequency charged. Some manufacturers offer 'frequency-agile' systems, which allow  the user to switch to an alternate frequency, saving time, expense, and frustration, These systems usually cost a little more, but the extra expense is worth it when you need to change frequencies and get back on the air quickly. Be aware that some radio stations are part-time, and may create interference that wasn't there when you tested the system.