Call interrupted by beep tone

during outbound calls from a sip trunk our agent suddenly hears a repeating beep tone and hangs up thinking they were disconnected. when i check the call records i see the person on the other end can still hear the agent while the agent doesn’t hear anything but a beeping.
So, actually it looks like the line doesn’t drop but some kind of interference takes place.
I also checked the full log file for an event at that exact moment the beeping started, but there’s nothing.
It seems that there’s nothing wrong with Asterisk.
So, i tried some different softphones but also nothing.

Anyone with a similar problem?

If every thing look good on the Asterisk side you might contact your SIP trunk provider or make a test with a different SIP trunk provider.

Is this possibly a second inbound call hitting the phone while the agent is already on a call?

If not, I would also suggest trying another phone, although I can tell you that in years of messing with dozens of different SIP phones I don’t recall a single one that randomly beeped, especially while on a call, without some explanation.