Final answer:
In Manuel's meeting scenario, the noise is his internal planning of his response, which distracts him from active participation and could interfere with effective communication.
Step-by-step explanation:
The source of noise in the communication scenario provided is d) Manuel is planning his response. In this context, noise refers to any interference that affects the message being communicated. While George's comment, Marion's sharing of information, and the participants' questions are all part of the active communication process in the meeting, Manuel's mental rehearsal of his response is a form of internal noise. It is internal because it is taking place within Manuel's own thought process, which distracts him from fully focusing on the current communication and can potentially affect his ability to contribute effectively to the meeting.