My DVD player really heats up discs? ?

I just picked up a used DVP-S9000es and I have run into a concern that I wanted to ask about. Discs get very warm after extended playing. This is true with SACD/CD’s as well as DVDs however; DVD’s get down right hot by the end of a movie. I have open front and rear ventilation but a half inch on each side. Has anyone else experienced this with their Sony 9000 DVD players? Is this normal?
I never had this issue with my 5 year old Panasonic player.

Thanks