Simply jack the rear end of the vehicle if you cannot fit under it the way it is. Put the axle stands under the axle housing. Get a friend to jounce and rebound the suspension. If the noise is happening that often and that easily it should be simple to pinpoint where it is coming from with your head under it.
This way there is no guessing games.
Although when you play guessing games this gives you the oppourtunity to replace unneeded suspension parts and the wife believes your just trying to fix something that is broken....
Maybe use my suggestion, find out where its coming from, fix that. Tell the wife you need to tub out the trunk and put all adjustable suspension components in. Maybe some mickey thompson drag radials will also assist in the squeak?? And when the squeak is gone after all that she will believe your a hero.... Win win??