Just to make sure what caulk is?

Idiot question I know but this is acoustic sealant right?. The stuff that comes in those tubes that go in that gun thingy? Thanks JohnG

You are correct - Caulk is the acoustic sealant that goes in the gun.

Yes, but within your choices for tubes to put in your caulk gun there are many different things. The main things that you are looking for is density, flexibility, and adhesion. You want density so that it is hard for sound to travel through it, you want flexibility so that sound doesnt easily travel between the surfaces being caulked, and you want adhesion so that it won't pull apart and form a crack to become a flanking path for sound. The stuff labeled 'accoustic' sealant meets these properties but you might find that so do off the shelf products that do not carry the special title.

Yes another name for Acoustical Caulk as we call it here is Acoustical Sealent as is the technical name on the side of the tube (I used the USG stuff)