Loud crash again

It happened again last night about 10pm. I was sitting in the den reading; my wife was using the computer in the library when a crash resounded throughout the house. This crash actually shook the house and jarred the cup I had on a stand beside the chair. A thorough search of the house and grounds revealed nothing, as usual. But the physical effects of whatever were certainly visible at the time. The pup heard it, ran to the western side of the diningroom. Certainly nothing visible in that area either.