When Tripod was a kitten he did the same thing except he did it RIGHT IN FRONT OF ME while my DH WAS SLEEPING IN THE BED!
I didn't realize it at the time, but there was something wrong. I will never know if that behavior was related. Maybe he was angry with my DH.???
It turns out that he had a rare type of tapeworm that is the result of eating raw fish that happens to have this worm. Nothing had been detected in his stool, but awhile later I saw the actual worm (yuck to say the least) while he was using his litterbox. It took many vet visits, online research, and treatments that didn't work before the right diagnosis was made. The vets office kept telling me that Tri must have been bitten by a flea because he had tapeworm. I kept telling them that HE DIDN'T HAVE ANY FLEAS! He had several doses of the usual tapeworm medication. The worm didn't die. Tripod had to have 32 times the normal amount of tapeworm meds (called Dronsit? or something like that) to be rid of this thing. This type of tapeworm is much stronger. Believe me, I did not like the idea of so much medication. The vet had never administered that much to a cat before, but we had no choice.
Like I said, it may or may not be related - just something to think about. I wasn't even aware that Tri had eaten raw fish until I thought about it later. He was found near my work, The guy in bay across the parking lot did a lot of fishing and would throw the remains in the trash. He must have eaten the fish before we found him.