The Unseen Presence Puzzle

Sometimes I am born in silence, Other times, no. I am unseen, But I make my presence known. In time, I fade without a trace. I harm no one, but I am unpopular with all. What am I?

A fart.

Explanation:
Farts can be silent or noisy. They are unseen but make their presence known through smell. Over time, the smell fades away, leaving no trace. While harmless, they are generally considered unpleasant or embarrassing.