Your instincts are good :-) That 'knot' - actually a wound in the tree - IS worrisome and it the soil level is too high.

The tree looks to have been telephone poled -- that is, planted so that the soil level is above the root flare. What you should be seeing at the soil level is the slight widening of the trunk as it develops into the root system. I'd suggest pulling away any soil or mulch so that this flared area is easily visible.

As to the knot.......there are various reasons trees develop these bark blemishes. It could have been damage by the growers as they harvested the tree, it could have been done during installation, it could be the result of sunscald or it could be an indication of some more perniscious disease issue. Is the area increasing in size at all? Does it appear damp or soft and spongey in the center?

Move the soil back and see how it looks. Get back to us with another photo of the base and answers to the above.

The wound doesn't appear soft - it feels hard on the inside. I don't think it's been growing, but I haven't really been paying attention. I'll keep a closer eye on it.

As I was pulling soil away this afternoon, I got about 1-2" down and found a metal ring running around the base of the tree, about 12" diameter. It was a little thicker than a wire hangar. It had parts that ran down into the soil, so I'm assuming it's connected to something below too. The picture I attached shows it after I removed it. Any idea what this is? Should it have been removed when the tree was planted?

Overall, I got about 4-5" down before stopping. I started hitting larger and larger roots. I'm not convinced I got all the way to the root flare, but hopefully it's an improvement. There were lots of smaller, hairy-like roots that I had to trim away. Anything else I should be doing?

Oy!! This not good. That metal is the remains of a wire tree basket that many trees are sold in. And yes, it should have been removed or at least cut away. Not removing these baskets has been shown to encourage circling roots, aka girdling, which can affect the long term health of the tree.

And it does look like you have uncovered the root flare, or at least most of it. Good. It won't hurt to go down a bit further and you can rake the soil away from the trunk for about 18" or so while you're at it. And cut off as much of the wire as you can manage, too. If you can dig down into the soil to get to the buried part without damaging any larger roots, do that. And while you are digging down, see if you can tell if the large roots extend outward or wrap round in a circle inside the wire cage. Hopefully, most will be going out and not around......around is not so good.

The tree was just badly planted to begin with......not your fault. Exposing the flare and pulling back the soil is about as much as you can do at this point (and removing the wire). Keep an eye on the wound - as long as dry and not getting any larger, it is most likely the result of damage that occurred when the tree was harvested or planted and nothing pathogenic.

Good luck and keep us posted.