That is when I discovered the sound was coming from a set of chimes hanging on the porch. Looking up into the tubes, I discovered a mud dauber building a nest. The reason I wasn't seeing the cause of the ringing was because the chime would only ring when the mud dauber was inside one of the tubes, so whenever I looked in that direction, there didn't appear to be anything going on.
I don't know why she decided to use the chime because it was certainly difficult for the wasp to get herself aligned so that she could get into the tube. She would hover forever trying to get in just the right position to grab the end of the tube. The ringing was coming from her wings hitting the walls of the chime as she climbed up to her nest.
Notice the thread-like waist which is indicative of dirt daubers (that one's for you, Dianne). They are solitary creatures and work alone unlike most other types of wasps. I swear it looks like she is carrying a little pear with a stem. To this day, I don't know if that was a piece of mud that just happened to look like a pear or whether it may have been some food she was going to pack in the nest. Look at how she holds it like a bag of groceries!
Finally. She got herself lined up and disappeared inside the tube. It was nice to know I didn't have tinnitus. That was then, this is now. I have developed a mild case of it since. Excuse me, I have to get the phone...