Using a 6300 w/ ATU, and noticed that if I'm listening to a slice and then zoom out or scroll, there will be some relay clicks from the 6300 and the slice reception will change (sometimes better, sometimes worse). Is it just a side effect of the ATU?
No, it has to do with how much of the band real estate it is processing and how much of that aggregate band pass the signal width your slice is sitting on occupies. You can use the question as keywords and add n5ac (whatever Steve Hicks call is) and Google it. He had a very descriptive explanation for exactly that phenomena some months back.