I have a Giant Roam 3 2018 that I got off Craigslist for $250. It had an issue with a sticky front tire due to disc brake caliper misalignment which I fixed today thanks to this forum. But I now discover that when I have the gear set to the middle chairing on the front derailleur it slips and grinds and I then have to give the left shifter a little half-click to get it to engage properly on that 2nd gear in the front derailleur. What's the usual culprit for this issue and what's the typical fix? It also occasionally makes a loud startling clank when shifting gears. This is my first decent bike since an old Fuji racer I bought many years ago and I want to get it tuned as perfectly as I can without taking it to a bike shop.