Tremor sound system issue

[DEF66]

My 2004 Ranger is equipped with the Tremor sound and is currently having an issue with both Right speakers, front and rear. I’ve checked the obvious, the balance on the head and everything is set properly. I have given this truck to my 16 yr old son and I was driving with him and put a Van Halen CD in the changer and noticed I wasn’t hearing the guitar solo on running with the devil. That’s when I started investigating. My concern is that both speakers are producing the same low volume and I’m not sure how this system is wired. I wanted to switch the L&R channels on the amp to see if it was the speakers or something else. My problem is that not much info is out there on the tremor. I have removed the cover and was attempting to open the black plastic cover to further investigate but can’t seem to get the plastic cover off. I have the 2 side brackets removed but it seems the brackets hold the entire unit down. The brackets are bolted through the floor and have to be removed from under the truck. It seems like the plastic cover should just snap off or just pull up but it feels like the amp and sub are still attached under the plastic cover or to the plastic cover. Any advice would be helpful.