You should use MLV w/ Closed cell foam underlayment underneath your carpet and padding. This needs to go wall to wall foam side down. Lead tape for the seams and acoustical caulk for the perimeter, you do not glue MLV w/ Closed cell foam down, you let it float.
http://www.soundproofing.org/infopages/flooring.htm What I would like to do is lessen the noise as much as possible in my bedroom. So would MLV under my carpet help any of this?
YES If so.
-Would laying the MLV over the carpet underlay be the same thing as using a MLV with an open cell backing?
YES and would there be a lot of benefit to using one with a closed cell backing for a higher cost.
YES because this has additional sound absorption foam-Also would you have to glue down the MLV?
NO-when sealing the MLV to the edge of the walls would there be any benefit to using green glue or would an acoustical caulking do the same thing?
Acoustical caulk is correct for this not Green Glue