When I lie flat on my back (and only at this time) when I inhale i make a weird thumping or hiccup like noise. It only happens if i am lying on my back. I have no other symptoms, no pain, no shortness of breath etc... I feel perfectly fine, am 40 y/o and in good health. This started about 2-3 months ago....I was researching and thought maybe it was a hiatal hernia as it seems like it's coming from my diapragm. Any ideas what this could be?