Confbridge injects noise in RTP stream


I have a specific conference scenario with recording in a production environment where for a conference with two participants are used two bridges. Each participant is connected in one bridge and RTP flows between the bridges. In this way, any participant will be able to control their own call recording.

The scenario is as follows:
Terminal1 <--------> Bridge1 <--------> Bridge2 <--------> Terminal2

When both terminals mute the audio, I can see that a periodic noise is added by the bridges.

In a capture, I can see that RTP that is sent by terminals is clear, but the RTP that is sent back to them has a periodic noise.

The following image shows the RTP streams:

The first and fourth RTP streams are the input streams (terminal to bridge), the second and fifth RTP streams are the output streams (bridge to terminal) and the third and sixth RTP streams are the RTP between bridges.

In the image, we can see that the noise is incremental, but the bridges seem to have some kind of protection that when it reaches some threshold it goes back to zero (Can I set this threshold?).

What is the cause of this periodic noise?
Is there any configuration on the asterisk that can I try to fix this behavior?

Currently, I use asterisk 11.3.0.

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