Hard to tell from that angle, but it looks like maybe an end panel failure. Did the installers place finished ends or did they come pre-finished? Does it move in and out a little? If it's a finished end-panel you may be able to doctor it up. You need some wood glue, a squeeze clamp with pads, and a couple of pieces of wood. First you'd carefully clamp a small scrap (about 3"x3") of plywood to the right hand edge of the countertop. If it goes up against a wall, just use the wall instead of a clamp. Then take another 3x3 piece of ply and place it up against that corner of the panel. Then measure the distance between the two pieces of ply and cut a skinny piece of wood about 1/4" longer than your measurement to wedge in there as a brace. Mock it all up dry. Then try to squish glue back inside of it as much as you can. Then clean it up with a damp cloth and make sure no glue comes in contact with the wood that will be touching your cabinet. This is very important. Once it's glued and cleaned, stick your wood pieces all together. Place the ply that's against the cabinet far enough clear of the glue that you can wipe any that squishes out. Keep it on for a couple of hours. Your cabinets should have come with a touch up kit that you may need to use. When you caulk it, apply a very thin bead and try to squish it under the cabinet as much as possible. I'd use clear silicone.

Oh my. Second thread in about a month with exact same scenario and exact same result.

For anyone planning a remodel, resist the urge to plant a linen tower on the counter. If you must, then plan some kind of riser made out of solid surface material or PVC to sit the cabinet on. Or hang it on the wall/ suspend from the joists with some space beneath it to prevent wicking.

Also, be hobest, how noticeable is it?

Four outta' ten noticeable. Meaning that I would definitely notice it; my husband would not; either that, or he wouldn't care.

That's right now; it's only going to get worse. Looks like the gable ends are MDF. Once MDF gets wet, it's done for. Crumbling, paint failure, yellow green mold yuck. (As far as cabinet materials go, there are only slightly better choices that might buy you some time and be a bit more repairable than MDF or particle board.)

dani_m08, did you notice this was a 6 year old post?