Knocking noises going over bumps can be caused by worn sway bar end links. These end links have small ball joints that become loose and rattle. Replacement is the only fix.
Problems for specific Volvo C70 years:
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Most reported 2009 Volvo C70 problems
The upper engine mount may wear prematurely. Symptoms may include a harsh feeling when the transmission is shifting and roughness when the engine is idling. Worn engine mounts should be replaced as necessary.