Moh in call when parked call retrieved

Hi,

I have a customer who has a busy pbx, every now and then when they retrieve a parked call they are hearing moh playing in the background, It is only the party who is retrieving the call can hear this, not the caller.

Has anyone come across this before? We have rebuilt the pbx on a new server and manually setup the same configuration and the issue is still the same.

This may be a user issue but I can’t see how they could cause this.

Thanks

Asterisk and freepbx versions?

Sorry I should have included that originally

Freepbx
PBX Firmware: 5.211.65-4
PBX Service Pack: 1.0.0.0

Asterisk
Asterisk 11.7.0

This issue was present on an older version also, pbx was replaced with this version of version, hardware and software.