I hear you loud and clear!

[Dennis Nemitz]

I was at the inspection of an up/down duplex that I have under contract today, and noticed that I could hear the inspector on his phone through the cold air return vent. I was in the downstairs living room, he was in the upstairs apartment bedroom. It was not muffled, it was clear as a bell. Do any of you have ideas as to how I can buffer the noise in those vents? I thought about a thin layer of spray foam insulation, but am not sure.