Has anyone else recently started experiencing a harsh static/distorted audio burst at the beginning of Retell phone calls when Background Sound is enabled?
My agents were working normally a couple of weeks ago, but recently I started hearing a very unpleasant burst of static/interference immediately after the call connects, before the agent begins speaking.
I did several A/B tests and found that the issue appears to be related to Retell’s Background Sound feature:
Background Sound enabled → harsh startup noise
Tried multiple background sounds → issue occurs with all of them, although some are worse than others
Tried several background sound volume levels → issue remains
Background Sound volume set to 0 → noise disappears
Background Sound set to None → noise disappears
I initially suspected Twilio/SIP/network quality, but the issue is reproducible and consistently disappears when Retell Background Sound is disabled.
Has anyone else noticed this recently? I’m especially curious whether this could be a recent change/regression in Retell’s background-audio mixing or whether certain carriers/codecs are having trouble with the background audio.
If you’ve experienced this, did you find a solution other than disabling Background Sound?
Thanks for your patience. We reviewed the separate audio channels and found that the agent’s speech track is clear, while the startup noise appears on the incoming caller audio track.
We’ve attached both recordings for reference. The left channel contains caller audio, and the right channel contains the agent’s speech.
Could you try one call with Background Sound enabled and another with it disabled while using headphones, and let us know whether you still hear the noise? If it persists, could you share a recording of what you hear on the receiving phone, along with the call IDs?
Hi Mark, sorry for the delay. I completed the additional A/B test using headphones as requested.
With Background Sound enabled, the harsh startup noise is still present and is very loud through the headphones.
With Background Sound disabled, there is no startup noise at all.
Both tests were performed using the same receiving phone/headphones and setup, with Background Sound being the only setting changed between the calls.
I’ve included the Call IDs for both tests and a Google Drive link of what I’m actually hearing on the receiving phone when Background Sound is enabled.
Thanks for completing the additional tests and sharing the Call IDs. I’m checking this with the relevant team now. As soon as I receive any update, I’ll let you know promptly. Thank you for your patience.
My test setup is an iPhone on the AT&T cellular network, using the standard iPhone Phone app.
I also tested from a second iPhone and was able to reproduce the same harsh startup noise. That phone was also on the AT&T network, so I haven’t yet tested from a different carrier/network.
On both devices, the behavior has been consistent: with Background Sound enabled, I hear the harsh startup noise; with Background Sound disabled, the noise is not present.
For now, I’m fine keeping Background Sound disabled on these agents, so this isn’t preventing me from moving forward. I mainly wanted to report it since the behavior appears consistently tied to enabling Background Sound on my end.
If it would be helpful for troubleshooting, I can also test from a different carrier/network when I have access to one.
Thanks for the additional details and for running the tests on multiple devices. I’m checking this with the relevant team now. As soon as I receive any update, I’ll let you know promptly. Thank you for your patience.
We reviewed the audio stream in the packet capture for the call and didn’t hear the harsh startup noise in that capture. We’ve reproduced it on AT&T but haven’t reproduced it on Verizon so far. Attached the audio stream screenshots for call_8d5bee9da677c6e00eaa6f2f7b1. (first is what we received, second is what we sent.) From the screenshot, we can confirm that the sharp voice is not from out end. This suggests it may be related to carrier.
For now, if the issue is still there and consistent, keeping Background Sound disabled is a reasonable workaround.
Thanks for the detailed investigation. That makes sense, and it’s helpful to know that your team was also able to reproduce the issue on AT&T but not Verizon.
For now, I’m comfortable keeping Background Sound disabled on these agents since that completely eliminates the issue and allows me to move forward.
I appreciate you and the team taking the time to reproduce it and review the packet captures. If you end up identifying anything further regarding the AT&T behavior, I’d definitely be interested in the findings.
Thanks for the detailed update. I’m glad you have a temporary workaround by keeping Background Sound disabled. I’ll keep an eye on this with the team and let you know if we receive any further findings regarding the AT&T behavior.
Thanks again for your patience and for helping us troubleshoot this.
