There are several options when it comes to the origin of the Morse code:
- UAs are made by 'the lost'. Basically, humans that are living in an unknown part of space. There are millions of potential lost people in the Galaxy.
- UAs are secretly made by a shady human group. The Dark Wheel, INRA and Sirius Corporation are prime suspects.
- UAs are made by Thargoids. They know Morse code and they know where we live. I that case, they are trying to send us a message. The Morse code is aimed at us.
In all these scenarios, the UA is manufactured. It's however still probably based on a living entity like the barnacles. A partly constructed, partly genetically modified being.
The 'last' options.
- UAs are made by another alien species, that has learned Morse code from our space junk.
- UAs are an autonome species (same as barnacles?) that has assimilated human technology into their being. They are able to do this because their metal-based biologi is similar to human technology. The Morse code is a leftover from this prosess.
None of these hypothesis stand out as very much stronger or weaker than the others. Pick the one that fits best in your tinfoil hat.