Do you think it’s due to the acoustics of my listening space?
My guess would be you’re sitting in a null created buy how both subs are interacting with your room and each other. Try playing with speaker positioning and your listening position and see if that changes things and/or reversing sub terminals on one speaker if possible. I don’t know how GoldenEar’s customer service is but I’d give them a call too as I’m sure they’ve run into this before. Best of luck.