I have a 2015 Specialized Crosstrail, and within the first 300 miles it developed a clicking in the pedals (not audible, just felt through the pedals), happening on most down strokes (both left and right pedals), and it also felt like the cranks were moving laterally a bit. Since I had one free tuneup at the LBS, I decided to take it in and told them that I thought the BB or cranks might be a smidge loose.

When they returned the bike, the mech said he tightened down the cranks. But when I took it for a spin, I instantly felt the same clicking exactly like before. In fact, it was getting to a point where hand turning the crank would yield the click feeling. I left it there again, and when I came back a few days later, they said they did some "adjustment" to the rear hub. I was a bit skeptical (thinking it was a bad BB), so I was pleasantly surprised that the problem seem fixed! I've only ridden it a mile or so around the neighborhood, but the clicking seems gone.

My question is this: What could be adjusted on the rear hub that would fix that clicking sound? Is it possible for the cassette to somehow get loose? The salesman that gave me the bike didn't seem like he knew details on what was done.