no, it's not coming from the back of the ps2, it's coming from the inside, through the grill in the front under the controller and memory card slots. It's an orange light.
If it were the harddrive (which g has explained, there is none) or even the modem (which we do have on it) the light isn't exactly direct, and i'll try and take some photos of it, and get them up (or have G do it)