Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
I am sorry that you have not been helped yet. I just came online and saw your question.
What you are describing is a faulty IAC (idle air control) valve. This is located at the throttle body. It has a pintle on the end that when it sticks will create this type noise/vibration and will cause a rough or erratic idle. I have uploaded a diagram of its location. You will need to replace it