I keep getting clogged injectors, when I sump the tanks in preflight I effectively never have particulate in the fuel. However, about an hour in to flight, I am getting clogged injectors typically on 3 and 4. After landing and trying to resolve the issue I am finding that I have particulate that is amber in color and feels like grains of sand in the tanks. What has perplexed me is the particulate only appears after flying the plane. Sumping the tanks, leaving the plane for a week and coming back