This question is more appropriately answerable by a private teacher or pianist friend who can watch / listen how you play and make qualified statements.
That said, it may be possible that because you are using a fourth finger (a weaker finger perhaps,) then you are trying to compensate by playing the chords more aggressively. It could also be a psychological trigger in which you see large chords so you play aggressively. Wind players often suffer from something similar - what we call "black note fever."
I would strongly suggest talking to a real person about this, but in the meantime you may think about playing through the chords as softly as you can, working on having all of the notes sound as evenly as possible.
Much like playing percussion (which the piano is much closer to,) volume is determined by the velocity of the strike, NOT the ferocity of the fingers. Playing loud isn't a function of slamming the keys, but rather increasing the hammer velocity with your fingers. Thinking about it this way can help reduce tension.
Lastly, I must suggest that the term "tetrachord" is more commonly used than "tetrad."