The generator matrix

 1  0  1  1  1  1  1  1  1  X  1  1  1  1 aX  1  1  1  1 (a+1)X  1  1  1  1  1  1  1  1  1  1  1  1
 0  1 (a+1)X+1  a (a+1)X+a+1  X aX+1 X+a aX+a+1  1 aX X+1 aX+a X+a+1  1 (a+1)X  1 (a+1)X+a a+1  1  0  X aX (a+1)X+1 aX+1 X+1 (a+1)X  1  a X+a aX+a (a+1)X+a

generates a code of length 32 over F4[X,sigma]/(X^2) who´s minimum homogenous weight is 96.

Homogenous weight enumerator: w(x)=1x^0+249x^96+6x^112

The gray image is a linear code over GF(4) with n=128, k=4 and d=96.
As d=96 is an upper bound for linear (128,4,4)-codes, this code is optimal over F4[X,sigma]/(X^2) for dimension 4.
This code was found by Heurico 1.16 in 3.24e-008 seconds.