I presume that by throttle plate you are really referring to the airflow plate; major difference. The throttle plate does not move at idle on cars with idle valves.
What you are seeing is the airflow plate deflecting in relation to the amount of air passing through. We will not be able to process the test info if all it contains is descriptions of noise. This does not approach test technique.
If you wish to view the problem you must use the right senses. Hearing is not the one. You need to visualize whats happening by viewing what happens under the terms confronting you.
Your valve is moved by a pulse width modulated signal. You need to use a pulse width modulated signal viewer. What ever it takes. The ears won't do it.
Bosch Master, ASE Master, L1
33 years MB technician