Strange Noises

Last night at about 9:45 I went to go read in our bed while Grant was on the computer. When I laid down I heard the strangest vibrating noise and the wall behind our bed was shaking. If I sat up I couldn't hear it anymore but if I was close to the wall it was really loud. I made Grant come touch the wall. I am sure he was wondering what was wrong with me and thinking I was going crazy until he felt the wall and yep it was vibrating. Immediately we thought it was our neighbors above us because they always have strange loud noises come from their house. I went up to ask and they didn't have anything on and they couldn't hear or feel the vibrating. Next I went to our neighbors behind us. Mind you it is after 10 by now and she is an older lady, her house was completely black. I rang the doorbell and no one answered, I decided to try one more time and this time I got her out of bed. I felt so bad but I was really worried that the wall was vibrating and felt like it was going to fall down. She answered the door and had us come straight in to her bed room and there was the problem.....A vibrating bed! (bad back). Anyway Grant had to pull her bed out from the wall. No more vibrating. Moral of the story don't buy a vibrating bed if you live somewhere where you share walls!!!!!!