Whenever you are transferring signals over airwaves, interference can occur, causing distortion and crackling in your audio output. Wireless microphones are versatile, portable and convenient, but should always be monitored using headphones to check for any interference. Wireless interference is invisible and can potentially ruin your audio. Even when you are certain no wired or wireless signals are in the area, interference can occur from the least-expected sources.
Direct Interference
If two wireless radio signals on similar frequencies are used within close proximity of each other, a direct interference between the signals may occur. If the interference from the other signal is stronger than your wireless microphone signal, a crackling noise could result and cause your audio to be unusable. Direct interference could come from a number of possible sources, including other wireless systems, communication equipment, digital devices and TV transmitters. Although this may not solve problems for stronger interference such as TV or satellite signals, it is best to set wireless frequencies at least one megahertz apart.

Electrical Interference
If you are using wireless microphones in a controlled environment without other direct interference signals, but are still hearing crackling noises, it could be due to electrical interference. Various types of higher-voltage equipment such as neon signs, lighting control systems and electrical motors can cause interference problems. Old equipment that has become poorly-maintained and is poorly insulated can be a major cause of crackling within your wireless mics. The signal interference can be avoided or fixed by moving the central control unit for your wireless microphones farther away from the problematic electrical source.

Non-Wireless Interference
TV and radio stations transmit powerful frequencies over a large area, and even the smallest stations can cause interference with your wireless microphones. Although TV and radio signals are transmitted wirelessly, these more powerful signals can jump onto nearby power lines. AM radio interference results in distortion of speech, and strong TV signals can cause buzzing and crackling interference. Powerful broadcast signals from nearby television stations and radar transmissions from electrical equipment can travel through power lines if they are close by. If you are using a wireless microphone outside near power lines that are carrying these broadcast or radar transmissions, it can interfere with your wireless audio equipment. The wired electrical signal can be stronger if you are near industrial areas where more power is being transmitted through power lines and can result in crackling, random bursts of noise and static.