This sounds like the next issue and would explain why that black box made it worse at my Grandmother's house assuming it's an amp.
https://www.tvfool.com/index.php?option=com_content&task=view&id=57#how_to_read
Be aware that amps and pre-amps will actually cause you to lower your Noise Margin. No matter how much gain an amp or pre-amp claims, it will actually reduce your Noise Margin by the amount listed as the Noise Figure (NF) in its specs.