Easy-peasy. What you're describing is a small change in the CV being sent to a VCA along with the usual level signals.
To do this, you'll want a sample and hold, and an LFO that's swinging over only a small span of voltage. Connect the LFO (even better if you can wavefold it) to the S&H "noise" input and then run the speed up considerably so that there's no real way to hit the same CV level each time it's sampled. Then, use an adder to combine the S&H's outgoing voltage levels to the usual modulation signal that you'd feed a VCA. If you then set up a second VCA to only open when the 16ths are being fed, that'll do it.