Not totally sure this is what you have, but the building code and the dryer manufacturers are very clear in stating that only rigid 30 guage glavanized metal pipe is allowed in the walls, crawlspace and attic (basically any concealed spaces). And absolutely no semi rigid aluminum flex or flex of any type in these concealed spaces. Flex pipe is only allowed as "transition" hose behind the dryer to connect to the in the wall duct system. So if you have crushed pipe behind the drywall, you may be referring to the alum flex pipe that is not allowed.
