Make sure you've got fresh batteries in the unit. Then see if distance between the transmitter and receiver is causing the problem. If you have more than one wireless system, make sure they are not using the same (or close) frequency settings (group/channel).

Most importantly, check for Radio and Television frequencies that might be conflicting with your system at:
www.shure.com
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You can find frequency confclits / recommendations at this link for all Shure wireless products including: SLX1, SLX2Beta58, SLX2Beta87a, SLX2Beta87C, SLX2SM58, SLX2SM86, SLX4, UC1UA, UC2Beta58UA, UC2Beta87UA, UC4UA, ULX1J1, ULX287JA, ULX2B58J1, ULX2B87AJ1, ULX2B87CJ1, ULXP4J1, ULXSP4J1,