Generating all possible combinations & randomizing their distribution in a matrix

I want to generate all possible combinations & randomize their distribution in a matrix.

Example:

Data Set: {A,B, C, D} String Length=4 (4^4=256 combinations)

So a 16 x 16 matrix would be generated & scrambled.

So AAAA AAAB AAAC... etc. would be randomly distributed within the matrix without AAAA or any other combination being repeated.

Ideas and links are greatly appreciated! Thanks!