Many things can squeak back there but, if it's truly sitting lower, start looking for a missing spring pad, or, ugg!! the rear carrier support bushings being worn out. Remote possibility might be a spring failure (unlikely)..

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.