The convertible top may have problems with the micro-switches and potentiometers that help control the raising and lowering of the top.
Several issues occur with the door locks on the Volvo C70 and most are because of the door lock assembly. What happens is that one door will not lock while the other one does. In other cases you will lock the doors and then one of the doors will immediately unlock.
The problem is that the door lock assembly is defective and will need replacement. Replacement of this assembly on the C70 is very difficult and is not recommended by a novice. Getting the door and window aligned properly so that you don't get air or water leaks is very, very difficult.
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.
The battery B+ cable has problems with the terminal end necessitating replacement. Symptoms may include no start, cranks wont start, warning lights coming on and other odd electrical issues. The B+ cable end is located in the engine compartment fuse box near the drivers side shock tower.
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.
The anti-lock brake system (ABS) warning light and/or other dash warning lights may illuminate due to a failed ABS Control Module . Replacement of the failed module is generally required to correct this concern.