It's the noise you make when you have an uncontrollably large and fully erect penis......so erect that it hurts and begins to bulge and pulsate. The noise is usually brought on by a so called "10/10" female or an "HBB"
Hnnnnnnnggg can also be brought on by things/pictures or items that you might not expect but are excessively pleasing to the senses of sight, hearing and on a rare occasion...taste.
<Kansas Misc Crew>
So, do you like.....workout or something?
No, I don't play basketball, anymore.
Yes, its proportional, but still doesn't look that big.