Have you tried a different cable? I demand that you do. And if you don't, I'll.... do nothing.
As mentioned in my first post, I have tried it out with a CDX, which uses a different cable, and still got the same results
. Also as posted, I get the same problem when using the Master System hooked up with the mono AV cables of my model 1 Genesis. I'll try messing with some other hardware too, like DVD players, PC-FX, SNES, etc...