I agree: A "sandpaper" feeling generally tends to be the side effect of calcium deposits. It could be something as benign as a build up of 6 years of usage in your lines that is finally purging itself from the system. Regardless of if it is or not you may want to clean out the lines using a specialized product to purge the system.
If it is a metal deposit as wmcall and myself have noted, citric acid (Vitamin C tablet, lemon/lime/orange wedge) would dissolve it. You can do a quick test with the aforementioned products. If not you'll need to report back to investigate further.