I've been struggling with this problem for awhile. Here is a curvature raster to illustrate the problem http://i.imgur.com/IIjYAov.jpg
I'm using 10m DEM rasters from the NRCS Data Gateway for a large portion of California. The problem is some strange tiling that appears after merging, but isn't present in the original data (before merging). The grids create low points, so flow accumulation etc is drawn into them.
I've tried mosaic to new raster, create raster catalog and filter in ArcGIS 10.2, merge and build vrt in Qgis2.4 but the problem persists throughout.
When the license frees up, I'm going to try Merge and Filter (production mapping) and see if that works.
Am I just merging files wrong? Are these edge effects from merging tiles?