Adding 3 bits of noise in a 8 bit word at random position. (VHDL)

I have created a Hamming code encoder to process a signal, up to here all good.

Basically I'm having issues to implement a "noise" into an output. For the noise, I want to apply up to 3 bits. I have to corrupt the 8-bit output by adding each of the 3 bits (fromo the noise signal) at random positions.

As an example: noise=111 and output=00000000. When the noise is injected into the 8-bit word, it'd look like this: 01000101/11100000/00101010... I've been trying rand() functions but I've had no luck.

I'd appreciate any sort of guidance here as I'm new to VHDL. I also find it difficult to find relevant info online. If someone could recommend me any other forums to gather more information.

All the best,

Pablo