Take you car to someone who specializes in car radios and sound systems. Dealerships do not necessarily have personnel versed in radio and electronic repair. In this case, a description of the noise, or better yet, actually hearing it, is diagnostic. Is it intermittent? Steady? A buzz or hum? Only make noise when the car is moving (could be the static buildup static shorting spring is missing in the wheel bearing caps, or loose connection disturbed by road bumps); sputs in time with the engine ignition. Since it happens for both the radio and CR player, suspect the final amplifer section and wiring and ground to the speakers. If you have an upscale sound system, likely, there is an auxiliary output amplifier somewhere that drives the speakers. This amplifier may not be under the dash. Favorite places are under a front or back seat and sometimes in the trunk. You'll need to invest in a good repair manual to chase it down. or buy service from someone who has the manual and knows how to trace problem circuits. Intermittent sputs of noise is often caused by loose connections, loose grounds, or wires broken inside the wire insulation. If the noise is limited to the door speakers, suspect broken wires inside the insulation and where the wire is flexed when the door opens. If the noise appears at all speakers, trace the signal wires from the radio to the amplifier; and check the power supply wires to the amplifier. The shop has replaced the radio. The problem could be in the remote amplifier if present.

time to move down

That would be electronic. Look at the cells carefully. Bent plates or large piece of dirt in the plates or broken ionizing wire would cause the arcing.

While allowed on the two small appliance branch circuits, deeding on what other loads you commonly use it might be better on its own circuit. A toaster or other large load just about maxes out a circuit. Add a microwave or convection oven, even a large stand mixer and you can overload. Like every induction, the refrigerator compressor pulls a significant start up surge. If the magnetron in the microwave cycles on at the same moment the compressor starts 20 amps may not be enough (even with the 'slow-blow' of an inverse time circuit breaker). If the refrigerator is used frequently every day the odds of missing the power being off are pretty small (unlike the freezer in the basement on its own circuit). Even a coffee maker is a significant load when it is brewing.