Buzzin pulse noise with manager api


I’m encountering a strange problem when originating calls through the manager interface. It doesn’t matter which program I use, astman, gastman, IPS, the results are the same. When i originate a call through the manager interface, the destination phone has an loud pulsing buzzing noise on it. I’ve tried this with four different phones, Grandstream GXP-2000, X-Lite, Polycom IP-501, Sipura 841, all producing the same results. However, when I originate a call to a Grandstream BT101 it works fine. When I originate the call from another extension directly to these phones without the manager api in the loop, it works perfectly, no noise and good connection quality. So, it’s happening as a result of using the manager api. Curious thing is, it doesn’t happen when originating the call, using the manager api, from one of the above mentioned phones (excluding the BT101) to any other phone. Any ideas anyone? Thanks.