Static noise from speakers/radio

Hello, I have a 2014 prius plugin base. When i bought the car, the previous owner had a subwoofer and amp installed. He had removed the subwoofer when i bought it. The car makes a static noise (like alternator whine for regular ICE cars) when it is turned on. Ignition on or full ready mode, it still makes the sound even when i push the volume knob to turn the audio off. Changing through the different source makes no difference. I went ahead and took out the wires from the aftermarket amp and the additional wiring harness from behind the radio unit, so it's pretty much stock right now, but the static noise still continues. How can I resolve this issue?

Additional info:
-There is a blinking blue light under the steering wheel towards the left near the parking brake, when the car is locked. This leads me to believe that there is aftermarket alarm system installed. Maybe that has something to do with the static?

-The static noise buzzes differently when driving, like as if its getting picked up by the electric motor. Sort of like an electric motor RPM noise.

-Previous owner said that the speakers were also changed.

Any help would be greatly appreciated in mitigating this issue.