I was quite surprised this morning to hear two shifts when I changed gears this morning... One from my bike and another one just a couple seconds later.... I looked back and was surprised someone wanted to draft me a the zippy pace of about 15mph. I just kept my pace and made sure I signaled when I was going to slow down/turn/alter course to avoid bollards/etc... I looked back a couple miles later and I was alone again. Who knows maybe I just hallucinated him?