I made an optocoupler by shrink tubing a generic photo resistor and a cold white led.
Then used it in the following setup to be able to control audio level to achieve tremolo effect:
However with each LED blink a brief noisy crunch is heard. I have no idea, but it almost seems that photoresistor generates a small spike of current. Can this be true? Why does that happen and how can I prevent it?
Unfortunately I don't own an oscilloscope, so I can't confirm my theory