I have an audio (mic, speaker) circuit that I am currently powering off of a 12V car adapter that is fed into a 10V switching DC regulator to power the rest of the circuit. I have noticed a horrendous amount of noise on the mics and speakers when running off of this circuit, even with the appropriate bypass capacitors from Vcc to Gnd in place, carefully tuning the DC-DC switching converter (buck-boost), and so on.
After breaking out my oscilloscope, it seems there is a lot of noise on the Vcc and Gnd rails that affects the entire circuit, and the noise is not present when I swap out the 12V car power source for an external 12V battery solution.
What would be the best approach to eliminating this noise source entirely? I am already providing a regulated power output, but it seems that the noise on Gnd is impacting everything else in the circuit, even with a regulated power source. I could create a separate Gnd for the rest of the circuit, but am not certain as to how this would work with my switching power supply if it doesn't share the same Gnd as the circuit it powers.
I have also considered using a flyback regulator, as it isolates the circuit it supplies via a transformer, but I'm not 100% sure if this will resolve the case of a noisy external Gnd.