How do I open model WMC6SB shredder (no make shown)?

My paper shredder has suddenly become very noisy. I have removed 7 screws from the base. I am still unable to prise open the shredder. In the center is an indentation with a melted plastic center. I imagine this might be where a screw is normally placed. I repair electronics and appliances and need to check the source of the noise. How do I proceed to open the shredder?