This is my first post. Can anyone help me understand what happened last week?

Around 3:00 am on Monday, February 9, 2009, I was awakened by 3 loud, purposeful knocks in the night. I had fallen asleep on the couch in the family room while watching t.v. (to my left) and awoke with a start. The sounds came from the kitchen(to my right), so I got up and said, "Is anyone here?" No response... no more knocks. My old dog did not respond. I am used to hearing occasional random sounds, because 3 cats roam around at night. These were LOUD sounds I never heard before... spaced about a second apart... not pipes... not animals scratching themselves and thumping the floor... not dishes in the sink that got bumped... certainly not sounds from the t.v. at the opposite end of the room. If I had to choose a word to describe the sounds, I would rule out thump, knock, or bump. It sounded more like... WHACK!...WHACK!... WHACK!

The next morning, I tried to recreate the sounds by experimenting with various objects. The one that came the closest to reproducing the sounds was a paring knife, firmly held by the wooden handle while striking the kitchen counter. My old dog still seemed oblivious when I tried this in the daytime. The cats were a little perplexed, but nobody was frightened. I often leave the paring knife out on the counter, because I use it so often.

It's a little unsettling to think that my paring knife could be making these sounds when nobody's there in the kitchen.
I googled 3 knocks and was surprised to see how many people have experienced this phenomena. Any thoughts?