High volume on first ring back tone calling an extension with Sangoma S505

Dear all,
I’m having a problem with all Sangoma S505 in my Company. I have 20 Sangoma S505 and the other phones are P315 (nearly 300).
Sometimes, when calling an extension, the phone makes a very high volume and a distorted dial ring back tone, very dangerous for the ear.
Only the first dial ring back tone is distorted, then the others are normal.
It doesn’t occur on every call, only sometimes.
It doesn’t occur when calling to an external number.
The call volume is set to a normal level, all the other sounds of the same call (other dial ring back tones and voice of the responder) are at a normal level.

I’m on PBXAct 16.0.40.11 and I try to keep modules updated every week or so.
The phones are on
Firmware (IMG) 3.0.4.91
Firmware (BOOT) 3.0.4.33
Firmware (ROM) 3.0.4.91

The problem doesn’t occur with P315 phones.
I have already tried to factory reset some of the phones, but with no avail.

Do you have any suggestion on where to look for to deal with this issue?
I suspect that is something on PBXAct side, maybe a setting on the phone EPM Template, but I can’t figure out.

I was lucky one day that I recorded this sound when making a call with speaker active, so I have an audio file I can send if it could be useful.

Thanks in advance.
Best regards.

Do you mean dial tone, or do you mean ring back tone?

Any dial tone when you first lift a VoIP phone off hook is coming from the phone itself, and that tends also to be true for ring back tone.

It’s actually the RING BACK tone yes!
Sorry for the mistake, and thank you for pointing out the incorrect wording.

I’m not english speaking and I don’t know the exact technical words in this field.

I made corrections to the title and text of my message.

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