Shock bushing failure in the rear can allow the shock absorber to contact the body and cause a squeaking noise over bumps in the rear. The faulty rear shock absorber bushings should be replaced.
Car Problem Reports
Mercury Mariner Squeaking Noise over Bumps in Rear
Mercury Mariner Problem
Visitor, 2006 Mercury Mariner, 101,000 mi
Ford TSB # 06-20-12...enlarge to 7/8" ( 22mm. ),( Unibit drill )holes at top of shock mounts ( rear ), install mod. upper bushings & wshrs. $36 parts.,Part # 7L8Z-18198-A ( 1 kit required ) Fits '06-'07 Escape/Mariner ( Tribute? ) built before 9/5/2006. Shock upper "stud" scraping on body "thru hole". High-pitched squeak/squeal, low speeds driving. No need to repl. shocks themselves.