This may seem like a strange question, but for my particular application we need to actually add synthetic microstructure noise to real time charts. The signal should still be representative of the aggregate market direction.
I expect that a good technique would be something related to signal processing in electronics or sound engineering. They have white noise generators that can be restricted to a band. I would rather something far less complicated though.
Is it perhaps good enough to take a random percentage of the actual change from the last difference?