To me, it invokes an image of something blocking your ability to actually see the other sources, more than drowning them out or simply being orders of magnitude greater. Almost an inability to measure them because of the objects interference. Not so much that it is a natural source of uncertainty you can't avoid but something not native to the experiment and imposed from practical restraints. Like you were trying to measure gravity with the big balls and some bastard installed a large cistern a few hundred yards away and won't keep you meaningfully up to date about how much water is in it at any given time. It's probably a perfectly fine choice of wording but without some more details I don't know.