How many miles on the cassette? How many miles on the chain? It may be its time to replace the cassette.
Measure your chain and see if it's "stretched" (actually worn) If you've ridden with a stretched chain it will wear out the cassette. And even with proper chain replacement cassettes wear out over time.
The fact that only the one cog is making noise, and it happens in each ring suggest that the cassette is worn, and its just starting to show up in that cog first.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.