1973 Build house. I replaced my toilet today. on removing the old bowl looking down past flange into the approx 3" pvc and just above the 90 degree curve, off to the side is an approximately one inch round hole clean through the pvc . looks clean cut. Toilet had been in use for 35 years several times a day with no leak and I would have seen as it is above a finished floor. I have had no recent plumbing or any work that could have cut into the pipe. Anyone seen such a thing before? is that some is of vent? Should I worry?

thanks for any informed thoughts on this.