Is it an infringement of copyright to add music to a slideshow of your own photos?

I do a little photography as a hobby (personal use only) and to make viewing my photos and my children and grandson's photos more fun, I add a song to the slide show. I do not sell the slide shows, use them for marketing in any way, or claim the song to be mine. We just like a little toe-tapping to go along with watching the photos as they pan across the monitor. I have done many of these slide shows without any problems arising from them until youtube decided one was a copyright infringement. ALL the photos were taken by me. It was only the song that wasn't created by me. BUT here's what is confusing...I had other slide shows created exactly the same way...a combination of MY photos and Music that I had on my computer.