The dealer was busy the day i dropped it off, so it took all day. However, as i mentioned that my squeak was fixed with the liner repair, it came back the next day. This weekend I decided that I was going to find/fix this sound myself. I had already diagnosed that it would happen on smooth roads at high speeds, and would go away if it rained.
I did some research online, and in older malibu's people were having issues with where the rear strut was seated on the body, and it was not lubricated and making sound. I talked to my dad about it, and we had an old cavalier that did the same thing. his friend (who owns his own inspection station) suggested that i pour a small amount of automatic transmission fluid on the strut mount from inside the trunk, and it would run down, and lubricate between the body and mount. I did that, and then sprayed the outer parts of the mount (in the well) with white lithium grease.
So far, its been gone. It didnt take too long to fix myself, and i didnt have to have go go without my car all day.