I had the same issue with my "late 2014" Macbook Pro. Just tapping the trackpad (or even dragging my finger across it) would make that annoying "tick" noise around the lower left hand corner.
I tried tightening the screws in the bottom case. I tried pressing down hard on the trackpad. Did not help a bit. Sometimes the noise would go away briefly however, conveniently enough when trying to demonstrate the problem at the store.
But I found a working solution!
Find a sheet of paper. Press the trackpad down into the clicking position, exposing a gap between it and the top case. Then simply insert the corner of the sheet of paper and pull it along the bottom edge of the trackpad once or twice. Done!
Not a permanent solution, but works every time. Guess it removes little pieces of dust or something.