This may be a stupid question, but here goes. I currently have 5 Tetra Whisper 40 air pumps on my 5 tanks. No problems, quiet. My question is: What is the difference between the UL Listed and NON UL with the exception of the actual listing? Are they constructed the same, same components? I normally buy the UL Listed version, but I accidentally bought one NON UL. Seems strange that they sell 2 different versions of the exact same product. Is it as simple as North American Packaging?