Noise in ceiling ductwork above return

[GRHooper]

All of a sudden we've developed a flapping noise in the ceiling ductwork that sounds like it is near the return. When the air stops, the noise stops. I am wondering whether anyone else has experienced this issue and what the outcome/resolution was? Thank you!

[viperjpm2]

We had several pieces of construction debris in ours, including some tiny pieces of electrical wire, Styrofoam insulation, saw dust... but it was aluminum duct tape (either scrap or came lose) that was half stuck near a vent - the movement from the air caused it to flap, for me it was a simple solution to just remove the vent cover and pull the debris from the vent, get out a flashlight and a mirror and hopefully its that simple for you too