Congrats on finding the source of your hum! I had a ground loop that was driving me nuts, and in turn I was driving my family nuts, before I found and eliminated it. Your search and destroy "mission" sounds like it yielded additional benefits beyond getting rid of the hum.

I agree with you that proper cable management just feels good. I got to the point I started making my own RCA type cables to get things neat and tidy. Its all good, and part of the HT hobby.

Before you permanently ban the use of your flood lights it might be worth it to look at the connections (in particular the ground) at the fixtures and at the switch to see if they are all tight. This is a real problem if you have any aluminum wire. I say this only if you are comfortable working with electric, otherwise an electrician should be able to find the source of the hum at the flood lights. Also, if the lights are on a timer or dimmer they it can induce a hum. Just some thoughts...