Hi!
Sorry for my bad English, i hope you can understand a little bit ... i have the same Problem here in Germany with a space grey iPhone 8 32 GB. I checked the Problem with the Crackling directly but in the first Moment i thought, the Telephone from my Client is bad. But then i noticed its a permanently Problem and i contacted Apple.
The Women there told me, they never heard about the Problem and then they want to sell me the Story, its because of the Weather she also has this Problem with a iPhone 7. But they offered me, that Apple will contact me 12 hours later.
So today i talked to a Supporter again, he also told me he never heard about that Problem and then he asked some Specialists at Apple with the conclusion that nobody ever had this Problem. It rembers me on VW and Audi, every Problem i had there is a sad isolated incident which only i had.
I told the Supporter that i restored my iPhone to factory settings, the first hours i had no Problems but after some hours the Problem was again there. Then the Support told me to check, if the Problem is my Backup, but the Problem is also there if i use a clean new iPhone without personal Userdata, without using a Backup.
I tried everything, resetting Network Settings also the global Settings, but nothing worked, its in all Networks from 2G, 3G and 4G LTE.
So now i had the chance that the Aftersales Team will change my iPhone into a new one, but like i understand the Supporter i must send them the old one and after that i get a new one. I also think i will have same Problem again after the Exchange like it was at the Antenna-Gate with the robotic Voice.