So I looked inside, and bubbles are being released around the base of the fill valve stem, where it sits in the tank. It makes a Passsshhhhh sound and does this about 4 times as the tank fills.

I've never seen this before...
So I checked under the tank and around the water lines, no water is leaking.
Next I searched the Net, but no one seems to have my exact problem.

This is our only toilet so I'm a bit nerviness. Is there anything I can do to troubleshoot this release of air bubbles?

Thank you for your advise.

What type of ballcock do you hhave?