I just picked up a South Park this summer. When I bought it I noticed a humming sound from the flippers any time I used them. The previous owner said it’s been like that ever since he’s had it and he also had it fully shopped before he sold it. I noticed at a local pizza place that their spiderman makes the same sound when you use the flippers. Is this something to be worried about or is this just common with stern/sega parts?