Set the current to either 3.6 or 4.6A, but start at 3.6A peak.
see if this solves the noise problem?
Regarding the software problem, this could be noise? make sure the RS232 cable is away from any power cables, and also make sure that your signal cables (Step, direction and enable) are well away from any power cables like the motor and the power supply cables. I cant see in the picture if you have done this. Also are the motor power cables shielded? and grounded at one end?