Question SMC3 Target Line Noise

Greetings All,
Long time lurker, first time poster. I'm in the process of building a 6dof flight simulator. It's powered by 3 arduino unos. I'm at the stage where I'm tuning the motors using smc3 util. Motors 1-4 are configured and behaving as expected. Motors 5 and 6, are giving me a bit of trouble though. These motors and the associated hall sensors are both connected to the same arduino. The blue target line for these two motors spikes at random, causing the motor to move erratically. See image attached for an example graph. The same is true for both motors. I suspect a grounding issue, but not sure. Am I on the right track here? Any ideas how to narrow down the cause?

Depending on the Hall Effect sensor you could be sending a PWM signal to the analog port. If that’s the case you need a low pass filter.

if you are using a knock off Uno the analog power might be bad. That would make sense that only that Uno has a problem.

Thanks Joe, I'll look into low pass filter. I'm certain it's not the arduino. That was my initial thought as well, it is a clone. But I replaced with a known good one and same issue. One other "symptom" I'm noticing is that smc3 util is extremely slow to connect to this arduino for some reason, 60+ seconds in most cases. This is true with both arduinos as well, generic and good one.