I got all my sites sounding good. Mitel has escalated my ticket to "level 4" or something like that. I'll be sending them freezes and logs on request.
DND, basically what I did at each site:
-Run Hybrid balance all loop starts
-Run Loop Loss all loop starts
-Re-start DB programming
-Go to the trunk(s) and note the Echo Return Loss (this indicates how clean your line is or how close you are to the CO card). If you are plugged directly into an Arris voice modem, you'll see this value between 0 and 10. This is a pretty clean line.
-If you have 0 - 10 for ERL, start On Line Monitor, pick a trunk to test and adjust the CO Receive Gain to +4 db. Adjust the CO Transmit Gain to -4 db.
-Run Hybrid balance test on that trunk
-Run Loop Loss test on that trunk
Re-start DB Programming. The ERL on that trunk will definitely change, but don't worry about that. Call into the system on that loop start trunk from the cellphone, and talk really loud into the Mitel handset microphone. Try to get it to produce static or feedback into the Mitel handset piece. If you still get feedback, hang up and lower the CO Transmit gain on that trunk one additional value (start with -5 db now). Re run the Hybrid balance test and loop loss test on that trunk. Rinse and repeat until the issue is gone. I never had to go below -5 db transmit gain on any site. Once it sounds clear regardless of speech volume, go to the Trunks and apply the gains that worked, to all loop start trunks and run the hybrid balance / loop loss tests on all trunks.
To run hybrid / loop loss tests on only one trunk at a time, click on Trunks and right click the trunk from the right pane to get the context menu.
On my sites with Arris modems, +4 Receive and -4 Transmit gain did the trick. The ERL on these sites was around 8 on all trunks. A couple of sites needed -5 db Transmit Gain to eliminate the static completely. These had higher ERL values greater than 10. If you have any questions feel free to send me a message on the forum.
Since Mitel escalated my ticket twice since I filed it, I suspect a fix may come out for this. Good luck!