OK, here's the deal: First, the original content said "chime played on the Montreal Metro" and then you edited it to say "sound made by motors". These are two different things. You changed content without giving any explanation or an in-line citation. The statement that your recent editing which removed content may have been unintentional, was simply a nicety to avoid any perceived insults. At this point, the statement should probably be removed simply on the grounds that there is no source citation and original research is not allowed.