Low spot in back yard got lower

In the back yard, by the back fence, a roughly 6'x10' area of ground seems to have dropped or settled a few inches. It's next a pole with underground power/phone/cable. There is an ice/water puddle formed there that wasn't there last year. From the grass I can see near the edge it does seem a little more sloped. A portion of the fence is also leaning a bit. I'll be more certain when snow is gone. Everything is working OK, but should I do anything in the spring?

 

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.