I have my old radio I was going to try that tomorrow. Don't have another mt4 I can borrow unfortunately.
The rx is mounted in the receiver box on a MBX7 Eco. Well away from the esc so that shouldn't be a problem. The motor has a sensor plug but I am not running sensored. Weird thing is that I did test the radio at a friends backyard track and it was all working fine. Race day today and I didn't finish a race.