Power rail oscillation during MOSFET turn-off
It looks like your AMS1117 is becoming unstable during the time shown. As this is when there are going to be transients on the output, any instabilities will show up here, even if the regulator appears ok at a static load.

The datasheet has this to say:


  Stability
  
  The circuit design used in the AMS1117 series requires the use of  an
  output capacitor as part of the device frequency compensation.  The 
  addition  of 22μF  solid  tantalum  on  the  output  will  ensure 
  stability for all operating conditions.


Your circuit has 1μF, well below the stability criteria. This requirement is not at all unusual for linear regulators (in particular LDO types).

Note that a solid tantalum device will have a somewhat higher ESR than a ceramic, which may also be assumed by AMS in the loop stability requirement.

A standard tantalum 22μF or larger (perhaps an ordinary TAJ series part) should do the trick. The datasheet explicitly states that a larger capacitor will simply improve transient response and not affect loop stability.

Another thing about the circuit is that most device manufacturers recommend a gate resistor (see figure 1) when using a totem pole driver stage as is the case here.

[Update]

Datasheet

This just goes to show that not all xxx117 regulators are created equally.

Useful graph on this type of LDO regulator:



What is interesting (this is the one from On semiconductor) is that a certain minimum ESR is required for all loads (and it is higher than the ESR most 22μF ceramics). 

[Update]

There are some excellent application notes on gate oscillation and how to tame it; even though the application ones I am linking are for high voltage devices, the fundamental information is still applicable.

Mastering the art of slowness

Mastering the art of quickness

Both from Infineon.