Flapping Noise in Intake

I have no idea what this is. I have recently noticed it after having the intake manifold gasket replaced. Does anyone know what might be creating this noise. It seems to be coming from the intake area between the engine and firewall.

Thanks for the help.

the upper plenum gaskjet may have slipped during assembly, and is vibrating due to engine vacuum. Also check to see if the pcv valve is in place. IF it popped out of its grommet, they will make a flapping noise also.