I'm asking everyone, with a 2013 Touran, why does it feel like the loudspeakers in the back don't produce any sound? Is there no loudspeaker in the back?

I have a 2007 Touran, automatic 1.8t. It jerks noticeably during acceleration. When idling while parked, the RPM intermittently drops by 100-200, and the car lights dim. What should I do? (I've previously cleaned the fuel injectors and throttle body.)