I'm doing a head gasket change, and while disconnecting the upper radiator hose, I noticed what looked like sand on the inside of the hose. On closer inspection, I noticed that there was quite a bit in the thermostat housing as well. Taking a close look, it appears to be rust mixed with little white crystals (salt looking). Should I be freaking out or what? I ran some Heavy deposit remover through the system last fall during the flush and fill. Did I just not flush it out good enough? Should I be concerned?