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  1. A brief burst of machine-gun fire was faintly heard.
  2. A brief burst of machine-gun fire was heard faintly.

Where should faintly be?

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anonymousWhere should faintly be?

Before 'heard'.

CJ

Comments  
anonymousWhere should faintly be?

Nowhere. Adverbs are deadly poison to fiction. Adjectives just make it feel a little sick. And the passive voice has no place in action.

 CalifJim's reply was promoted to an answer.