Yes, there will be some power noise from the ESCs, especially when the thrusters are run in air.
Yes, the largest spikes are due to regenerative braking. This cannot be disabled completely without modifying and compiling a custom fork of the BlHeli_S firmware. You can fine more information in this thread, I expand on the explanation in my last post there.
You can use a power filter to attenuate these spikes, a low-pass RC filter is a good place to start.
Normally, these variations are not an issue. Just out of curiosity, what exactly is your application/setup that makes this a concern?