Loud screeching sound heard when calls are transferred to outside number on FreePBX system

We have a phone system on Integra analog lines and a TDM800P analog card with hardware echo cancellation. The phone system we are using is a FreePBX box and Asterisk 1.8. When users try to transfer a received call to an outside number, once the transfer is completed a very loud screech is heard and one person can’t hear the other. However, if I program a ring group in the phone system to call out to an outside number and users transfer to this ring group, everything works fine. Three-way calling works fine as well. It seems to only be manual transfers to outside numbers. No other FreePBX system using analog lines has this problem so I’m stumped. I have run yum update and tried switching the trunks from DAHDI to ZAP compatibility with no luck. The phones they are using are Polycom SoundPoint IP 501 telephones. Does anyone have any ideas on this?

Have you run fxotune and balance your hybrids.

Thanks for the response. I have run fxotune, but I’m not quite sure what “balancing your hybrids” refers to.

Please read the fxotune documentation for an explanation of what fxotune does, the correct usage and how an analog hybrid operates:


I’ve followed the instructions and run through the process, but I am still receiving the high-pitched squeal only when calls are manually transfered to an external number.

Any other ideas on this one?