Curved black frame on Sony?

I have a 13 year old 27" Sony Television it is a Trinitron Model
#KV-27TS32 which has served me very well over the years but about 2 days ago it began having a curved black "frame" on the sides and occasionally the bottom of the picture which of course elongates images on the tv show. It is very annoying, I am thinking it is the Tube but I really have no idea. I do have digital cable also so I don't know if it could have something to do with that.