Bed Shaking

[IcedMoonlight]

Many times before i have been laying in bed and my bed begins to shake. not like its banging against the wall type shake, but you feel the vibrations of it moving. It nots cause by something else in the house..no washing machince or dryer or anything like that. I have NO idea whats causing this. A few times its even happened and i asked my husband "do you feel that" and i made sure i didnt specify anything, and he replied "the bed shaking?"..its happened with or without him there.