'fax machine' sound when asterisk answsers on zap channel

i have an asterisk box set up with two pstn lines for inbound calls on two zap channels (i have a tdm400 card with two fxo modules). i have two voip lines for outgoing calls.

the issue that i’m having is kind of strange, but i’m getting a complaint from my boss who calls in constantly (he’s a micromanager…sigh). he says that if he calls in 3 times back to back, there is a kind of ‘fax machine’ sound that he can hear over the autogreeting. i would assume he means that there is a high pitched tone that sounds.

i don’t know if this tone goes away after a time, or after you make a selection, i haven’t been able to replicate it to test it. but he’s had the problem on more than one occassion and continues to point it out to me.

does anyone have any idea what might be causing this, or what i can do to track down the issue. i’m not even sure where to start looking really.


so, i was just able to replicate the issue that was being reported. i called my incoming line once, hung up, then called again right after and i was able to hear the squeeking ‘fax machine’ sound. i could still hear the automatic greeting behind this abnoxius sound, and it did eventually go away after 5-10 seconds. everything seemed to operate normally otherwise.

i also tried calling in on one line, and while still on the first line, i called in on the second line immediately after. this did not cause any issue for me.

it seems like its an issue of a call coming in on a zap channel immediately after someone has hung up on that channel, as if it hasn’t had a chance to properly hang up or whatever it needs to do…

anyone have any ideas or troubleshooting tips?


i’m still having problems with this and i have been unable to find what the exact issue is. help please…