OK, a more useful observation/inquiry.
When you merged, what did you have the Deghost Amount set to? Deghosting is not perfect, and can lead to issues. When it does, try less deghosting.
In my test, I went all bonkers and set deghost to high, and a circle of noise occurred much like your issue, same location, circular. (might also be a bit on the left)

Mind you, your friend appears to have moved a bit, so no deghosting will not work. Try low:

Mind you, just some quick tonal adjustments, so take the results with a grain of sand.