I am using RegionPlot and I want to use Opacity for the color transparency

RegionPlot[x - 3 Sin[y] < 0, {x, 0, 4}, {y, 0, 3}, PlotStyle -> Directive[Blue, Opacity[0.3]], BoundaryStyle -> None]

But when I save the result, it contains some random grid lines inside it; how can I get rid of them? I need a clear plot.

enter image description here



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