Choppy call quality with only one caller/east coast callers unable to call in

Hi, there knowers of VoIP. I have FreePBX running on a VMWare VM w/ 2 CPU, 3 GB, and a 50 Mbit asynchronous fiber line with ALG disabled on our Sonicwall. Phone system is working very well when dialing into conference lines, making phone calls to cell phones, etc.,…for the most part. One caller in particular with a Salisbury, MD number, every time her and I talk on the phone there is a choppy sound during our call. I do not get this when I make an outbound or receive an inbound call with east coaster located in the DC area on her mobile or office lines.

I suspect that I’m dealing with a codec issue during negotiation between the two system when experiencing the choppy calls. Thoughts?

/var/log/asterisk/full logs would be a good start. SIP debug if that doesn’t help.