A few months ago, I had a high-pitched whining noise whenever I started the engine. It could last for just a second or up to a few seconds. I had the starter replaced, but that did not solve the problem. They did something with the tensioner (don't remember the details) and that solved it. However, the last day or two, I've noticed the sound starting to come back. Does anyone have an idea on what might be causing this? (I should add that the engine starts fine.)