It is allergy season. It is mucus from your sinuses running down the back of your throat. When you exhale, the mucus vibrates. The mucus runs into your stomach, so it should not be a problem. Now if you are having trouble breathing while you hear that vibration, it may be a sign of pneumonia.
You shouldn't worry too much. Like I said, it is allergy season, and everyone is getting. In fact, when I lay down, I get a cough because that darn mucus likes to slowly roll down my throat. I suggest you take some anti sinus medicine and listen to Chuck Mangione's hit album "Feels So Good". Chuck's music is always cool and refreshing. Chuck's album makes the perfect workout partner.
Feels So Good by Chuck Mangione