Both my wife and I have HTC10 phones on Verizon that just recently updated to Android 8 (Oreo). After the update, but wife's phone kept showing the "Location found" notification and playing the default notification sound. It was incredibly annoying because it did this every few minutes or less. Well I performed several different Google searches to find an answer and all of the posts that I found never actually provided a solid answer on how to fix the problem. Well, I'm creating this post to help others because I finally solved the problem!
On my HTC10, this is what I did to fix the problem: Go to Settings -> Sound & notification -> Advanced -> Notifications (at the very bottom).
Then click on the three dots at the top right of your screen to the right of the search icon. Choose "Show system".
Scroll down the list and find "System UI" and select it.
Choose "VZW" in the list and once you get into the VZW notification category for System UI, click on "Importance" and change it to "Medium: No sound". This will turn off the notification sound that plays when your phone is finding location.
You can also turn off the notification icon that shows up at the top of your screen by turning off the "Allow icon badge". I actually just left this turned on and now when an app requests a location update, I see the icon pop up at the top of my screen, but I don't hear that annoying sound.
I hope this helps all of the other people on the numerous other posts I found about this topic that never received a solid answer on how to solve the problem.