Dry gurgling from shower drain
If the shower has not been used for a long time, the water in the P-trap under the drain  will evaporate, so you no longer have a seal against the sewer lines. So anything else that drains into the sewer will make sound that can now come back through that shower drain. That by the way would also be letting sewer gasses back into your house, which is not good. Pour some water into that shower and see if the sound goes away.