Lots of masking going on in old basements with dirt floors. Lots of iron and bits of metal, wire pieces and who knows what.
As you know, if the house is wired and powered up it can interfere with your detectors abilities. Older homes had plank flooring without tongue and grooves. There were spaces between the floorboards. If a coin was dropped and rolled, many times falling through to the basement floor, never to be found.
Over the years, many owners of older historic homes had their cellar floors lowered, digging out the old dirt (tons of it) and actually spreading it on their property. Any treasures went along for the ride.
In the next week or so I have a job of shoring up a floor of a home that goes back into the early 1800's. Its a crawlspace (yuk) but I will be packing my detector. The homeowner has stated that her family has lived there for generations. I hope to find something that will be of some meaning to her past.
If you have the time and patience, remove the masking culprits, you may be in for a find of a lifetime.