Very well could be the hops settling in it. It has a way of causing degassing and release of the CO2, hopefully not oxygen, in the beer. It is perfectly normal. But do make sure you take gravity readings a couple days apart before you bottle to make sure.
Bottled: Dark Skies Black IPA, Sunrise Honey Rye Pale Ale, Yooper's Oatmeal Stout
Kegs: None owned....yet
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