Arrived to remedy a strange noise potentially coming from the hvac system. Homeowner said the noise hasn’t occurred since Monday night. Walked around system and tried to recreate the noise. Found a duct not perfectly mounted to the wall. Secured the duct in place. Went outside to scope out the roof. Was unable to find a specific cause of the noise. After writing up summary for the office a manager had a suggestion to check the fireplace damper. When checking this damper moved the bar to close the damper and did not exactly recreate the noise, but made a very similar noise. If there was a wind or a draft, the damper could have moved and made the noise in question.