A [Very] Rough Approximation to "White Noise" with Sine Waves
Phase and amplitude of this sinusoids should be random, so you need Gaussian random number generator. If you don't have the random number  generator then might want to think about implementing one, here is, I believe, the most popular algorithm: Box-Muller transform.

Depending on your application and device, you might also want to use other noise source (i.e. Online generators, highly amplified signal from a probe).