Hey folks, I've got a Swinger II with and e50 and this high pitched ringing noise has been bothering me since I restored it 2 years ago. From what I remember, I replaced all the bearings and seals. I'm thinking it could be any of the following: worn gears, worn bearings, worn brass bushing, or an air leak somewhere. Bike is all stock except hi flow air filter from treats and a larger jet (probably too large). I noticed some oil on the underside of the engine so I may need a new exhaust gasket. My friend has the exact same moped as me, with his being 100% stock, and his sounds much quieter with no ringing/whistling/whining whatsoever. I've attached two videos of the sound, one with the bike stationary and one in motion with the camera in a backpack. You start to hear the sound at about 0:26 in the video.
Thanks for your time, guys.