T21P-E2 nonstop beeping

[JoseVM]

Hello. I have a few T21P-E2 phones that all of a sudden started making this beeping sound every 10 seconds or so. I did a factory reset, checked out that MWI was disabled, and stutter was set to 0, but it didnt work.

I have call recording but there is no rule to make this beeping sound every 10 or 15 seconds in my carriers admin portal. What else do you think I can do to stop this?