Hi,
all three suggested reasons can be true. In my opinion. feedback supression is worst. This gives a warbling, chorus-like sound. Let your audi turn off feedback-supression and see if that helps.
Interference between direct and amplified sound occurs, too. For me I hear this especially with my own voice when I talk outdoors with wind. But this is rare. Only means against this would be a closed fitting (which has other disadvantages).
Compression gives me a kind of “chopped sound” when I am in bigger halls. This goes away when I use my live-music program (which has less compression).
Some of those artifacts you’ll have to live with. I decided I didn`t want to live with the artifacts of feedback supression, so I turned it off in all programs. But I do have feedback sometimes, which is annoying. It’s a matter of compromise.
Good luck with improving your settings,
Musician_72