Users of older wireless microphones could soon be hearing unexpected sounds on their systems.

In just over two weeks, radio microphones will no longer be allowed to operate in the 698-806 megahertz range.

Those frequencies are being re-purposed for 4G telephony.

Len Starling of Radio Spectrum Management says it'll soon be difficult - and illegal - to operate microphone systems in that range.

"Those systems are getting increasingly noisy and they may well at some unpredictable moment cut out or stop working."

Starling says microphone system owners need to check their frequency, and get them re-tuned before March 11.