Probably isn’t a vent stack but it couldn’t hurt to check to be sure you don’t have some dirt dobbers or a birds nest
Is the noise coming from the wall or the toilet itself ?
Does the noise stopped after the toilet reservoir downstairs refills ?
If so my guess would be the fill valve is malfunctioning and needs to be replaced
Is the noise coming from the wall or the toilet itself ?
Does the noise stopped after the toilet reservoir downstairs refills ?
If so my guess would be the fill valve is malfunctioning and needs to be replaced