The wave: I will admit this one was a direct copy - because it was, imo, a good question right in the path I was thinking of. This was the only question I deliberately copy-n-pasted. Someone commented on the source during the challenge was taking place and that sparked many other solutions that were semi-copied from there.
Morse code: That was my first question, and was completely original - nothing inspired it. I did not know of golf.shinh.org when I started.
Musical notes: This was indeed inspired by the link you gave, but it's reverse, not to mention the note structure is different as well (that has impact on the solution by a large degree).
Sierpinski’s Triangle: Was not deliberately copied from golf.shinh.org, it was my own idea and I actually ASCII'd the solutions in gedit. It was one of my first ideas (it was about to be posted after Morse code) and was saved for an 'emergency' I-ran-out-of-ideas.
Seven Segments: Same as Morse code - I was not aware of golf.shinh.org at the time. Also of note that this question is reversed, which changes the answer by a really large margin. It was also my first and only question I added a restriction, and people did not like that (I was trying to discourage the use of figlet related libraries/services).
As for source attribution for code golf - as much as I love giving credit where it's due, I think it ruins the fun. People go - check out - and ruin the solution for themselves. Mostly because those sites contain answers already. While not a direct copy of challenges (regardless of 'The wave'), I think that it would spoil the fun for those who really want to try. Remember humans - by nature - are very curious creatures, and saying stuff like "Just don't click the link" will encourage clicking even further :)
As for the other questions - they are completely original - Lasers, Beehive, Playing cubes, Hourglass and Spider webs - all original, and were inspired by my personal life experiences.
If the community does, however, "force" me to put sources, I will change every question that has a semi-direct relationship that I know of, will get added and posted in the future.
Personally I would hate it if I was forced to put a link to 'related' questions - I think it'll spoil the fun.
I only knew of two direct attribution links - The wave (was indeed a direct copy) and Musical Notes (Provided inspiration and guideline, I had an early idea about notes already).
Another thing to note is that The Wave has the most answers of all my questions (at time of writing)! This confirms my concern that giving the source (if applicable) will ruin fun and increase participation at a cost of ruining people's fun.