Rattling on start (during summer) + battery being constantly charged?

Hey all,

I've been chasing a bit of a phantom issue for a bit, and realized I may have TWO issues now. I'll try to break it down as much as possible.

Firstly, the car has been a little rumble-y when pushing the power a little past the middle line on the power indicator. When I speed up or slow down, the rumble goes away. Lately though, the car rattles VERY hard on start. It was so bad that the engine light came up. Mechanic said spark plugs, we swapped those out and now it just rattles to varying lesser degrees. The rumble during drive seems more pronounced.

In addition, the power flow screen shows that the battery bank is doing very little. The car seems to be incessantly holding the charge at around 75%. The engine will be funneling power to the wheels and the electric motor, and the electric motor will be almost nonstop putting power into the battery despite it being nearly full.

My hunch is my EGR is getting bad and maybe my hybrid battery but I'm not sure.