Sangoma S505, S400 static on call

Recently most (if not all) series S phones have static on two different systems. Among the many things I have tried:
reverting to a different phone firmware: from IMG–3.0.4.91 to .67 and everything in between
turning off auto-update/auto-provision
(all those suggested thru different searches)
turned ON edge mode

finally I turned on a different version of freePBX:

Current PBX Version:
15.0.17.24
Current System Version:
12.7.8-2012-1.sng7
Total Module Count:
114
Enabled:
113
The numbers below may be inaccurate if new modules have been released since the last check: Last online check:
2021-04-03T07:28:10+00:00

and the phones (3 phones that I’m testing with) worked and sounded fine (same trunk settings)

on the newer (and active) freePBX, the phone’s sound quality is bad:
Current PBX Version:
16.0.40.8
Current System Version:
12.7.8-2306-1.sng7
Total Module Count:
122
Enabled:
108
The numbers below may be inaccurate if new modules have been released since the last check: Last online check:
2024-06-11T17:45:44+00:00

I took a phone,S505: Line 1 is connected to the new PBX, Line 2 is connected to the old PBX. Same phone. static on line 1, Line 2 sounds normal.

Series P phones work fine on the same servers (P310,P330)

Any help/ideas?