I recently had the 'crashed UFO' event, after finding the alien and disabling his radio the Garbled Broadcast continued playing. It appears there is a bug related to Relay Tower 1DL-109.
"If the alien is killed prior to extending the satellite, turning off the ham radio will not make the signal go away from the Pip-Boy. This also happens if the satellite is extended prior to the crash event. Solution: Turn the ham radio off and back on, go to the relay tower and extend it, go back to the cave and turn the radio off."
"Signal from ham radio after killing alien prior to extending satellite appears fixed in v1.10.163.0 (Steam).[verification overdue]"
"Steps taken: Killed alien, turned off ham radio, turned ham radio back on, extended satellite, turned ham radio off, signal disappeared."
I followed these steps and it solved the problem. The weird thing is that I had previously extended the radio tower, but when I returned it was lowered.