My return air duct spans 2 joists in the basement. This means that the metal of there is a sheet of metal nailed to the bottom of the 2 joists and this creates the channel for the air return. The question I have is, with me planning to attach drywall to the bottom of the joists, is this going to create some crazy sound transfer into the air return and essentially into my HVAC system? The reason I ask is that there is an HVAC guy coming to the house today to service the system (its going to be 90+ on friday and the thing doesnt blow cold air right now), so I figure if it is bad to have things the way they are, I can have him redo the return duct in the theater where it is tucked in a bit from the edge of the joist. this would keep the drywall from being in direct contact with it, which if it is an issue now for sound being blasted through the HVAC system, I would hope that it would be solved by spending a few buck to have him re-do some of it.

Here is a photo that kind of lets you see what I am trying to talk about:
http://i206.photobucket.com/albums/bb60/smakovits/P6030319.jpg

Mine is the same and it seems like there is a little more sound transfered through in that location than in other parts of the floor.

You could probably put linacoustic liner in there and it would help. I'm not an expert like Dennis e. though.

The extra sound that comes up through isn't THAT much more really.

I guess I will leave it in place the way it is then...thanks guys. if it isnt going to make much difference then whats the point of fixing something that isnt an issue