PC Engine coregrafx possible problem

[Manhattan Sports Club]

I bought a PC Engine Coregrafx from eBay recently which came with a stereo AV cable, which I switched with my Genesis model 1 mono AV cable that has the same input. This is because there was some slightly noticable bar of noise going from down to up when using the stereo AV on the PC Engine, and the switch of cables reduced it almost entirely. I am wondering if this is normal? It's only barely visible when the screen is entirely black, and not really visible during gameplay. I am using a 3rd party AC, which says:

"AC/DC Adaptor
I/P/AC: 100-240VAC
50~60hz
O/P DC: 12VDC 1A"

In case that affects anything.

On another note, I don't get the same effects when using the stereo cable on the Genesis. Both are relatively cheap cables.

[Manhattan Sports Club]

Pfft, I think it might be the TV, because I've tried both cables on another TV and both give me little interference, though the barely visible rolling line is still there, but at the same time I don't know if its normal or the precursor to a bigger problem, someone here let me know.

[Manhattan Sports Club]

So a little update. I was testing this out again, and here's what happens: When I have both the AC and AV plugged in to the outlet/tv, and the system turned off, I get those faint lines rolling across the screen, however, I pulled the AC out and it disappeared. Again, like I said, this was all while the console was turned off but was fully connected regardless, so I guess it was still outputting to the TV. What do you suggest I do? Get another AC?