This feels like an episode of Car Talk, but can I ask you, are they stockinette cardigans?
Because I find that in some yarns, when I knit plain stockinette, especially in the round but also when I knit it flat, the fabric "biases"--i.e., it is kind of slanted in one direction. I always block this out, but as we know, blocking doesn't really affect the structure of the knitting, and it can wear off.
I know there is wisdom out there about why stockinette biases for some people--I think it has to do with knitting looser than you purl or something like that? Bueller? HALP!
Does it make a noise when you go above 30 mph? (More Car Talk lol. Miss those guys.)