House was built cheaply in 1959, 1 1/2 story. Entryway added on in 1970. Over the past 4-5 years, whenever any of the exterior doors are closed or slammed the whole house seems to rattle and shake asif it is loose from the foundation. I recently replaced all the exterior doors and the rattlesand shakes are just asbad as before. Where should I start to try and diagnose what is wrong?