A defective power steering return line can cause a knocking noise when turning or going over bumps, especially when the engine has reached normal operating temperature. The power steering return line should be replaced.
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Newest reported 2007 Mercury Mariner problems
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.
The transmission oil cooler may develop a leak, which will require replacement to repair.