Small "carbonation" like bubbles in fermenter??

I brewed a 10 gallon batch which I put into two 6.5 gallon carboys. After 7 days I racked one carboy into a 5 gallon secondary which was nearly full leaving only a small bit of head space. Fermentation was slow by then but still active. 3 days later I dryhopped both carboys. the 6.5 responded as normal but the 5 gallon began fizz like crazy with lots of tiny bubbles like I had salted a coors (I've never actually done that). It over ran the airlock but settled down in 5 mins. or so. I cleaned that up and all seemed well.

Tonight, day 13, I took a gravity reading and in the hydrometer tube the beer was bubbling as if off gassing like a freshly poured beer???? Gravity was 1.008

It tastes fine, good in fact! No sourness or bret that I can detect.

What the hell?????

I had the exact same thing two batches ago. As soon as I put my thief in, carbonation started bubbling out like crazy, and the sample inside the thief had a tall head. Same thing in the hydrometer tube.

It's normal. I can't exactly explain all the conditions that cause this to happen, but the basic premise is that the yeast is creating a ton of CO2 during fermentation, and if the conditions are just right a large quantity will absorb into solution. Nothing to be worried about in my opinion, my beer turned out fine.

It's CO2 coming out of solution. When you add something physical (salt, wine thief, dryhops, etc.) you're creating many new nucleation points, which provide physical points for the CO2 to come out of solution.

Same science behind a dirty glass causing foam, and many breweries' new laser-etched beer glasses.