I'm having the exact same problem and it's definitely related to the last update since it was working fine before applying the update and started acting like this right after.
Also tried every single step to fix the issue to no avail, also tried using the google phone app and the exact same happens.
On receiving a call the caller says they hear a strange noise and nothing else, if I toggle the loudspeaker on and off then it starts working properly. The same behavior happens in both samsung's phone app and google's phone all so it ain't related to the app itself.
Hope someone can shed some light on how to fix this issue since it's annoying to always have to toggle the loudspeaker on and off to be able to receive a call.
I'm using a dual sim from two different network operators and it happens in both so it most likely isn't network operator related either.
EDIT: just checked the s9 forums and a bunch of people are complaining about the same problem, so I guess it's related to the 9 series. One of them, however, reported he received a new update this last saturday that solved the issue, fingers crossed it also reaches us soon and also fixes it.
Yeah, it's not a perfect solution but allows to make a regular phone call meanwhile until they sort it out.
As I said on my last edit to my last post they seemed to have pushed 2 extra updates to the s9 series which seem to have solved the issue this last saturday, so let's hope they release one for the note soon as well!