There are sounds from frequencies that most people can’t hear. She could legitimately be hearing something from the basement wall like she says and it could just be an electronic that is emitting the noise and y’all just can’t hear it and she can. It could literally be driving her crazy. Especially since she seems to not be hearing it now that y’all are not there. The fact the old owner won’t answer is suspicious to me as well why would she be ignoring your calls and not returning them unless she knows something is going on? Good luck op hang in there and don’t give up on your wife.