Team spokesman Reggie Roberts says the team became aware of the league's investigation during the 2014 season.
"We were informed during the season that the league office is looking into crowd noise during our games," Roberts said. "We have co-operated fully with them, and we're awaiting the outcome."
The Falcons could be fined or penalized with the loss of a draft pick if found to have added fake crowd noise during the opposing team's huddles of when trying to call a play.
The investigation was first reported by ESPN.
The Falcons say 100 of 102 games have been sellouts since Arthur Blank bought the team in 2002. Actual turnouts declined during losing seasons the last two years.
Atlanta ranked 10th among the 32 NFL teams with its average home attendance of 72,130 in 2014. Construction is underway for a new $1.4 billion stadium which will replace the Georgia Dome in 2017.
NFL spokesman Greg Aiello on Monday said the league had no comment on the investigation.
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