Often when this happens, it can be a mod conflict which causes the issue.
This can be a conflict between a scenery, or AI livery, or basically any addon that did not come with the base sim.
Another thing you can check is to what is selected under General Options - Sound, check to ensure that Main Device Output and Communication Device Output are both selected to the same source as your PC’s selection.
In any case, I wouldn’t be too concerned unless it continues to do so on a regular basis.