At 9 kilos, you're flying close to the specified max of the Aero 30. Is your sled fully extended? My experience with the Zephyr is that if you fully extend the small-post-diameter sleds (standard procedure if you're flying big weight), your going to frequently get vibration like that.
You can easily check if it's your camera plate. Try jiggling it with your fingers. If it doesn't move, it's not the plate. Do the same with other components on the top stage. If they don't move, they are not the problem.
if you suspect your post is vibrating due to being fully extended, shorten it for this load by adding more weight to the bottom. Bongo-tie or gaff tape some weight to the bottom where the sled is still in static/dynamic balance, but the sled is not extended at all, or only slightly extended.
I got around the problem on my V-mount Zephyr by adding a 2-into-1 battery plate (aka, hot-swap plate), so I could add 2 batteries, adding more weight to the bottom of the sled. I then used two large (240 wh) V-mounts with the plate. That enabled me to fly a fully-built Red ONE camera without the sled extended at all.
My vibration problem went away.