Figured it out.

Customer had requested that calls ring-no answer to voicemail after 5 rings. We approximate a ring to be about 4 seconds.

So, we had set the Delayed Call Forward timer to 20sec. But the Transfer Recall timer was ALSO 20 seconds.

Since a call from the AA to an extension is a transfer, it seems it was trying to transfer to the users extension, and also recall the transfer at the same time resulting in a brief no-audio message.

Increasing the Transfer Recall timer to higher than the Delayed Call Forward timer fixed the issue.

Just an FYI incase anyone else comes across this.

Cheers.