Using an FFT to identify noise
"tick" sounds are usually created by something close to an impulse, or with a significant portion of impulsive energy.  And time domain impulses create broad or wide-spectrum noise in the (FFT) frequency domain.  So you are unlikely to be able to find or remove the majority of this noise with a generic (LTI) filter, such as an EQ or a notch.

If the sound was more like a hum than ticking, then you would have a better chance.

You might instead want to try putting some ferrite beads on the wires from the source of the 12V transient signal.  Or wind those wires through a ferrite toroid.