I am generating smoke from particles (and coloring it). After the smoke is emitted it looks fine but the source is generating strange straight lines. Even when reducing the Density Scale it simply lowers the opacity of the whole thing but the issue is still there.

Are you hitting the edge of your smoke object's container? The automatic resizing node sometimes needs some adjustments and may accidentally clip your sim at the edges.

ianoreo
Are you hitting the edge of your smoke object's container? The automatic resizing node sometimes needs some adjustments and may accidentally clip your sim at the edges.

No, I already thought about that, it has ample room, in fact the padding I have is a little too much but I kept it like that just to be sure.

Maybe the smoke color is (far) too bright as compared to density. You could try adjusting the color ramp, taper off the ends or similar.

All right I found the problem. You see I was sourcing each smoke trail from a single moving particle that I Rasterized, when you do that houdini simply creates a square volume (it's size is @pscale) around that particle, now if your smoke Density Scale is too high or if the brightness is too high then the edges of the generated square will begin to show up.
The solution is to not source from a single moving particle but from a sphere or some other geometry. Then no matter how bright your smoke is no artifact will show up.
Thanks everybody for your help.