It might have some effect, though  this is not a true 
  isolation transformer
  
  
  
   This would be the more 
  likely candidate, let me know if you get it and how well it works. I'm in the 
  market as well due to the crappy old wiring in our house. It also occurred to 
  me that it could very well be caused by wireless interference or perhaps a 
  neighbor operating a ham radio or heavy machinery like an arc welder or 
   big electric saw. Do you have any big power lines or microwave towers 
  near by?
   When I was recording at 
  the Technical Institute Studio in Istanbul with Erdem, They had an isolation 
  transformer the size of an industrial refrigerator, and we still had some 
  radio interference. Is it possible you have right wing extremists operating a 
  pirate radio station near by?  hey it doesn't hurt to ask:-)
  Bill