How do you know if you tivo hdd is "going"

Have had my Tivo Series 3 HD for probably 8 years. Have an external HDD hooked up.



So lately live shows are locking up or pixellated. Doesn't happen all the time. Over the past month A LOT of the recordings are have the same problem and it is really ruining the watching experience.



So my question is...Is it most likely the tivo hard drives "going" bad? Or is it more likely the cable (Comcast)?



I have another Tivo HD XL in my bedroom and it doesn't seem to have the same issues. Granted that one is a couple years newer and doesn't run on the same cable line into the house.



Thanks!