How to reduce vibration of quadcopter

We have experience with some significant vibration of our customized quadcopter.

Frame: DJI D330
Flight Controller: CUAV Nora
This is the look of our drone:

This is how to mount the flight controller:

One of our flight test video, you can see the drone is shaking (very small shaking in propeller and arm):

This is our flight review log:

Could someone provide any suggestions on how to reduce the vibration for the drone? Will changing the propeller size solve the problem, and also what causes this kind of vibration?

Thanks in advance.

judging from the pics I’d say most likely all those wires and connectors and tagged-on parts rattling around.
You’ve got to think of a quadcopter as four powerful shakers connected trying to fly…
Try reducing connectors where possible, shorten and tighten down all the wiring etc.
Did you soft-mount the flight controller?
Once everything is mechanically as sound as can be you can try reducing the PIDs from default, specifically lower the P value on each axis by a good chunk.