a repeating sound file would get pretty annoying after a short while, but a dynamic generated sound might not be. there could be a brush stroke sound which could be generated to change texture and amplitude with the pressure and speed of the pen/mouse stroke, and the material which the brush is moving across. dabbing would generate a sharper sound depending on the pressure, speed, and material also. different tools and their different sizes would have different sounds also.
of course this is unnecessary to the outcome of the artwork, but a bit of fun never hurt anyone. plus it would be a great challenge in programming, and very original. This has been the computer scientist in me talking, so i might even have a go at trying to develop something like that if i ever have some free time. could be fun.
I think, therefore I am..... I think.