It's lucky for you that we're not skunked by this one. There is nothing worse than having a dinner guest go off to powder her nose only to wonder if your home has been selected as a community landfill site. Needless to say, when the guest returns from the bathroom with her hair uncontrollably limp, you have a serious problem that deserves immediate attention.
We first suggest that you consider not ever hiring again the gentleman that snaked your pipes. It sounds as if you have fallen victim to the old rupture-the-vent-line-while-snaking-the-pipe-routine. In simple terms, the vent pipe (the vertical pipe that carries sewer gases from the plumbing fixture up and out through the roof), was probably ruptured when your sewer man snaked it. The fact that he was banging for almost an hour is evidence enough that this is the case. Fear not, this can be one of the simplest and most inexpensive plumbing repairs you'll ever have the opportunity to make, especially since you will be completely remodeling this bathroom.
First, you will need to expose this vent line by removing the interior wall covering immediately adjacent to the vent pipe in question. Once visible, a quick going over will expose the damaged area. Unless the damage is extensive, in which case you may need to remove all or part of the pipe and replace it with a new piece, an inexpensive rubber compression repair sleeve will do the trick. Most major hardware stores or home improvement centers will have what you need to make a proper repair. By all means don't wait too long to make the repair. This condition could hinder your ability to attract and maintain friends.