It does sound like settling but could also be frost heaving. Often when a trench is backfilled, it may react differently as the frost is leaving the ground.
I roll my yard in Spring while the ground is still sopping wet and then plug aerate after it dries up a bit. I then redistribute the plugs, taking them from the high spots and leaving them in the low spots. I also top dress with compost which tends to go on a little thicker in the low spots. After repeating this for about 20 years, the results are noticable.