A truck carrying cars is not an aggregate though, at least not in the same sense here. A flight of geese would be closer to a decent concept of aggregation I think.
The UA change is good except I would invert the colors. This one makes it look like an emitter in the sky under a rain cloud cover. Or, maybe put some sort of simply boat to show it's water.
To get some more inspiration, I have attached two alternative pictures.
I don't associate aggregates with groups of people and I like to see some water in the underwater acoustics icon.
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