Static on sip Trunk

Why would there be static on a sip trunk ?

I double checked the phone and it only happens when you call in and not call out and it doesn’t happen between phones.

Just outside callers.

Is there anything that would causes buzzing or static to be on a sip call ?
it boggles my mind considering that the whole thing is digital just about.

I have a Grandstream phone which gives me static through my headset. I have to click to speaker and back to headset to make it go away. It only happens on inbound calls, never on outbound.

No clue what it is, but it definitely something in my phone.