Grounding a Powered Subwoofer Causes Volume Increase

UPDATE:

I discovered that banana plugs fit perfectly in stereo-mini-plug ports.  This subwoofer has a stereo mini-plug input that I am never going to use.  So I changed the spade to a banana plug and now I am sending any signal or noise that touches the stereo mini-plug port to shared chassis ground (which also connects to various ground boxes).

@gdnrbob 

Yeah, that would make sense. On the Audioengine HD6 and A2+, they'd have a faint "hiss" when they were on and no audio signal was present. This hiss would go away once audio was present and wouldn't appear in quiet moments in a song.  Audioengine claimed this was normal as the hiss was representative of the constant power being used.  On a subwoofer, it cannot "hiss" but that doesn't mean there wasn't some form of signal in constant use when no audio signal was present. On the HD6, that hiss disappeared when I grounded it, so it's entirely possible I did the same on the sub.

No experience with the equipment you use/d, but when I demoed another grounding unit, I noticed a subtle, though noticeable increase in the 'blackness' of the system-like, less noise in the background. 

Perhaps this is what you are noticing.-Maybe not increased volume, but enhanced definition.

B 

@russ69 

I think I figured it out. I am not certain, but I think I nicked the volume knob slightly when I was attaching the ground.  Whereas that would better explain the volume increase, it wouldn't explain how bass at that volume was not distorted as it had before, which is why I set it to the volume I had it originally.

Why doesn't it need grounding? I contacted Audioengine and their engineers said all their analog amps are single-ended.  That means only one input is handing the audio signal and the other is just a ground loop.

I have no clue but if you are adding grounds to something that doesn't require a ground, I'm thinking you should know the answer to that question. I don't know what is going on but something is and that may be important. Call the sub company and ask that question.