Function series with the "rand" function (Matlab)

I am writing a code for a sum of functions, where each iteration is slightly changed with a random number:

S1 = symsum((exp(10in(1+0.01*rand)*sin(x))),n,0,19)

I use symsum because this appeares the best choice for function series. However, the result graphs that I get look too neat and I suspect that rand works only once for the whole sum, Is it the case? and if yes, how to fix this?

Thanks in advance