When I turn my hot water on at the kitchen sink it recently started coming out instantly hot. I used to have to wait @30 sec or so. Now I have to wait 30 sec or so for the cold water tocome out. I also noticed the floor tile in front of the sink for about a foot is warm. There is also a little hissing noise under the sink. No visible water leaking under, around or outside near the sink.
What could this be?

You have a leak in the pipe, under the floor.