Noise generator type hiss on every 3rd or 4th voicing even when noise is off

Is that an indicator of a faulty voice chip? I picked up a prophet 6 and the aftertouch was disabled so after a lot of trouble I got the guy to give my money back. I did notice when I was playing it that a loud hiss would happen on every third or fourth note played. I turned the noise generator off and it continued to be there. I couldn’t find any way to control it. Admittedly, it sounded cool and I was thinking maybe it was intentional to add some “vintage character” to the synth, but upon seeing that there’s no way to control it, I’m feeling suspicious. Also when I would power the synth on, it would make a loud tv static sound (just like on the 3rd or 4th voice) for a second. Then everything would be fine and normal. Was there something faulty or is that pretty normal?