Singing cats

Question
We have 2 Persian cats, brother and sister from same liter.  Both cats have been fixed.  About 3 years ago the male cat started singing.  He will never do it in front of us. Usually he sings at night, he will away from us, go into the hallway and start singing.  
Some time later, it seems he taught his sister to start singing as well.  Although it is some comic relief, and usually not for long periods, his timing is impeccable.  Often it's right when we're about to watch TV or have sex.

We think it can't be for attention since he usually leaves the room with us to do it.  Our other guess is it's happiness or the equivalent to singing in the shower.  Halls have more of an echo.

We've tried researching this on the Internet but do to the common practice of making songs with meow recordings, it's impossible to find info.  Recently, a neighbor (who is an astro geophysicist) suggested we trt searching under "cat singing behavior"  I just did this and that's how I found this website.  But I still haven't found any info remotely connected to why would a cat sing.  I have friends that have had cats for over 20 years and they all say they've never seen this behavior.  Please let me know of any info you're aware of regarding this.  Thanks.

Answer
Hi Joeseph,

Some cats like to sing. I have a couple here who do this during the day. I have one that when she has a toy in her mouth she sings. I think she is just telling everybody about her kill. Another of mine sounds like he is telling me all that went on during the day. I think it is a way they are communicating to us.
About the only thing I can think of to do to get him to stop is to tire him out so he sleeps during the night. Cats sleep a lot during the day and sometimes are very active at night. You have to change his sleep patterns a little. I would play with him during the evening. Get a laser pointer and have him chase the red dot all over the place. Get him some fuzzy mice and tie a string on them . Again have him run around after them . Try what you can to get him moving in the evening. Also you can try to keep him somewhat active during the day if you can. See how his singing episodes are like after trying these things. Good luck and let me know what happens.

Ciao, Karen