I'm troubleshooting a system that is being bombarded with EMI. So far I've found a few basic design no-nos that should help mitigate the circuit's susceptibility to the EMI, but, I'd like to confirm some other items that I'm a bit fuzzy on. Measurement setup: Scope with 4GHz SE probe reference tied to regulator output reference signal tied to regulator output leads as short as possible, difficult due to location, but i'll accept some noise due to this limitation. Probe offset set to 3.3V During EMI: VCC swings between 6.6V and -6.6V. Investigation shows nothing to clamp the output of the regulator, so my first thought is a uni-TVS. My question is, how can I be sure this is "real"? Also, unfortunately I cannot probe in parallel close to the load, so it's LC filtering may be slowing the energy induced and be somewhat stable. Without being able to see what the load sees, would you agree a TVS at the load would be a good idea to ensure whatever noise is present is clamped to the best of our ability?