I saw a tweet concerning a current flight for DOJ aircraft N721AL. It's en route from Key West, FL to DC. Actually, just landed in DC at 1:25pm Eastern.

I didn't think much until I googled the model of the plane "De Havilland Canada Dash 8" and looked at it's WIKI page.

Could be nothing but it includes line "The Q Series are post-1997 variants fitted with active noise control systems."