What is this? Is it Bipolar? BPD? Nothing???

Today my husband was whistling so I asked him if he always has a song in his head. This sparked up a conversation whereupon I found out that he can his mind can be silenced. I was shocked (call me naive), but I figured this was only possible while meditating. Not just a normal thing - to have quiet inside your head.

I then told him about my mind. I'm not sure if this is also a part of my racing thoughts because I think of those more as actual run on sentences telling me something either true or imagined. I always have a tune in my head. Whether or not it's a song I know, something unknown to me, or possibly even just 3 random notes that play in an endless loop. A lot of the times I find it as numbers. Sometimes beginning at 1, other times completely random sequence. It will usually consist of no more than 10 numbers. But again, it's played over in a loop in my head. There is never any "silent" time up there. The numbers or tune will then be interrupted by a thought or whatever...always to come back. It's annoying and has been going on for as long as I can remember.

Does anybody else experience this? My husband thought it was different. I assumed that everybody's mind dis this or similar, I now know that to be untrue. You learn something new every day.