You may just be picking up on the extremely low fidelity audio of the speech from that era. Back in the 80s memory for audio samples was so limited that Williams had to compress the hell out of the voice clips in order to fit them onto the rom, often causing certain frequencies to be almost entirely lost ("s" sounds in particular are rather difficult to hear on system 11 games). Unless it is an unusual amount of loud static whenever voices are played, it's normal. Could you post a video with sound?