There is no way that 5Amp motor controller should make such terrible noise that affects even your TV screen. This is simply telling you, that your design is badly screwed. Not many people have actually any knowledge how to design power electronics.
So at first, get rid of those silly copper pools. They are useless.
Second, the power circuit should look like this and not else. The decoupling cap shoud be electrolytic, designed a chosen based on current ripple. If you cannot use big enough electrolytic anywhere near, use there 1-2.2uF beefy MKP (polypropylene) foil cap, 100 to 250V rated an then place the electrolytic somewhere near.
Third: Make sure the mosfet is not switching too fast, otherwise it will produce a lot of unnecessary noise and EMI. At 20kHz, you can sure leave it switching slower, that means to use higher value gate resistor, about 100 ohms. The switching loss therefore increases, but at 5 amps current, it is no issue, the power loss increase will be small. Advantages are reduced EMI, which is what you want.
Proper frequency. If you regulate the motor at 20kHz, it is okay. Some people actually think, they can use any frequency, which they want. Not true. The frequency of PWM should by f >> Us / (0.4 * La * In), where Us is the supply voltage, La is the inductance of the rotor winding and In is the nominal current (rated) of the motor. (Some math and thought going on, I don't want to dig into that now) Usualy the minimum frequency is in the range of a few kilohertz, but for practical reasons, it s used higher, so you can't hear the PWM sound from the motor. And also there is no reason to raise the frequency too high.
The circuit should look like this. For example there is an 555 timer as a controller. It is also useful to put a RC or better an LC filter between the fat power supply and the control circuit, so the noise and ripple from the power stage do not enter the controller circuitry so easily.
The loop consisting of diode, decoupling cap and mosfet shoud have the minimum possible length of trace. Lets say 2" / 50mm max. Any length extra wil degrade the performance and adds EMI, because HF ringing can occur in the circuit.