The airwaves turned blue in Mansfield town centre when scores of shop security walkie-talkies appeared to blast out the sound of two people having sex, as red-faced customers listened on.
The special communication devices are used by shopkeepers to keep in contact with each other, usually to share details on potential shoplifters.
But interference picked up the sound of suggestive moans and groans to leave shoppers embarrassed and shopkeepers clambering for their volume buttons during a recent weekday morning.
It is thought up to 150 shops in the town, including some of the large high street chains, have the devices.
One town centre shopkeeper, who did not want to be named, said it happened around four times in 10 to 15 seconds bursts.
He said: “We first heard it mid-morning, and whoever they were they both seemed to be enjoying themselves.
“We thought it was somebody mucking about and thought it was hilarious.
“There are some shops around here that have their radios in the staff room but others have them turned up so the customers can hear it.
“We laughed about it but I can see that it could be embarrassing for others.
“We had one bloke walk in to our shop while it was on and he said ‘at least someone’s enjoying themselves!’.
“At one point, the security guard said (over the airwaves) ‘Whoever it is, you are either having a really good time or in serious distress, could you tell us which one it is’.
The communication system in place for around 18 months, courtesy of Mansfield BID who seeks to promote the welfare of the town’s businesses.
The unnamed shopkeeper said: “The radios are great and they’ve been a massive help. They’re a cracking bit of kit to keep us in touch with the rest of the shops, but this is the first time anything like this has happened.
“It’s not something that’s going to stop us using them!”
Dave Wilson, BID business crime manager, played down the incident, saying: “It has been reported to us that an external radio using the same frequency as radios in the town centre may have been broadcasting potentially inappropriate and sensitive material.
“We have been in contact with the radio operator and are satisfied that there was nothing untoward going on.”