9v huh?
You’re running off of a single 9v battery, aren’t you? (I can just feel it).
Beyond that, this also feels like motor noise to me. Stick with what others have said, need to see video, etc. --but in addition, I think you need some caps on your motors. Just some basic, .1uF caps on your motor terminals. Just pick a LMR post at random and you will probably see the caps on the motors and how to connect them.
In addition, a big polarized cap (the one with - marked on one side (round, like a can)) on your power lines may help as well.