Mytoilet is making a bubbling sound when no one is using it.

That can happen when you have a clogged vent stack. No one is using that toilet but they drained something somewhere else in the home and the air vented through the toilet because the stack to the roof is clogged. Rod the stack from the roof with enough snake to reach roof top to basement floor plus 20'.

It's not often I disagree with Bob but this is one of those times.
Let me explain. When you have a blocked vent draining a fixture sets up a vacuum. Since the vent can no longer pull air the systems attempts to vent itself by pulling air through an trap. Hence, a "gurgle" is heard as the air passes through the trap seal.
When you have a partial blockage the discharge runs down the drain line, hits the clog and bounces back sending a "bubble" of sewer gas ahead of it. Hence your "bubles" . Sounds to me like you have a partial blockage downstream from the toilet that must be snaked. This can be snaked from one of two places.
1. From the lavatory roof vent. **OR**
2. Pull the toilet and snake from there. Good luck, Tom

Tom is likely correct but the OP needs to better explain the issue. When someone tells be they see bubbles I follow Tom's thinking. However, when they say a bubbling sound I then take it as possibly a gurgle. Poster, do you see bubbles or just hear a sound?