It's possible that the chattering noises could have been misinterpreted for interference on the medium wave which many Radio 1 listeners were still relying on for coverage, with the new FM signal of the time still not yet covering the whole nation.
It's possible that the chattering noises could have been misinterpreted as radio frequency disturbance on the medium wave, which many people were using to get Radio 1 coverage, with the new FM signal still not covering the entire country.