A United Airlines Holdings Inc. (NASDAQ:UAL) flight reportedly returned to Bradley International Airport in Connecticut after losing part of an engine liner, adding to a series of mishaps this year that have placed the airline under regulatory scrutiny. The Airbus SE (OTC:EADSY) A320 aircraft, en route to Denver International Airport, experienced abnormal noise shortly after departure, according to a Federal Aviation Administration (FAA) statement, reported Bloomberg. United confirmed that a piece of a sound-dampening outer liner was found on the runway post-landing. No injuries were reported,…