Hi I had a look and listen at your video. You will always get a single 'thump' on the audio when the call button is operated/released. Multiple thumps as shown on your video is wrong. Do you have the audio line termination components fitted at the power supply end? Is your power supply adequate? If your power supply is marginal, it may be going into current limit and the output voltage dropping when the call button is operated. This is much more likely if you are using a switch mode power supply (which the background whine suggests you are). Try a different power supply. Regards Peter