Voltage regulation circuit 12V to 5V in 5A range

[amgen]

if you didn't already........ put your probe lead on 'ground/negative' at a distance from the negative/ground probe connection..... and probe to various ground/neg locations. Sometimes noise is 'introduced' into circuits from other sources called common mode noise.....
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Key Takeaways

Noise appears in two forms in an electrical interconnect: as differential mode and common mode noise.
Differential mode noise is measured between two sections of an interconnect with equal and opposite polarity, while common mode noise applies to interconnects with the same phase and polarity.
Both forms of noise are induced in an interconnect via Faraday’s law from external radiation.