I've been trying to locate the source of a loud squeak/chirp in the rear of my VX for weeks now. I read up on previous posts and one mentioned the transmission mount on the cross-member may be loose or missing bolts/nuts. Turns out only three bolts were holding the cross-member to the frame and they were all loose, and no nuts were holding the trans mount at all. I replaced missing hardware and tightened everything down but this was not the source of the squeak. Doh!
Someone drove me around so I could sit in the back to track it down. That didn't work because the noise wasn't present when I was in the back. Must be related to the suspension then since it goes away when more weight is in the back. So, I sprayed silicone on all the bushings underneath. That didn't help either. Finally while driving and reaching into the back until I found a likely vibration. It was on the forward cargo strap shackle. I removed both and the sound went away. Turns out the bolt that was holding them on was about 1 1/4 inches and would make contact with the top of the fuel tank on bumps. Put a 3/4" bolt back in and wonder full silence. Well, actually now I can hear my exhaust leak better.

No, I am not obsessive!