I have a 3 year old toilet and just within the last month the tank has been emptying and filling backup all on it's own - if I'm home for 4 hours straight, I'll hear it 4-5 times. I did replace the wax ring awhile back. Is it water pressure or a leak? Thanks in advance!

I have a 3 year old toilet and just within the last month the tank has been emptying and filling backup all on it's own - if I'm home for 4 hours straight, I'll hear it 4-5 times. I did replace the wax ring awhile back. Is it water pressure or a leak? Thanks in advance!
It sound like a leaking valve in the bottom of the tank.
Remove the tank cover and inspect the water level for drainage. The lower valve may be out of position or the float device may be restricted in it's travel.

Trick my son does, take the top off the tank ( back part) put in a little food color, if the color starts showing up in the bowl, it is leaking though that little flapper. These get bad very often, and sometimes just do not seat right or get something in it.