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.
The possibility exists that the chatter might have been mistaken for radio frequency disturbance on the medium wave, a common source of interference for Radio 1 listeners at the time, who were still relying on this method to receive broadcasts, whereas the new FM signal had not yet reached the whole nation.