simple, straight lines?

I'm having difficulties drawing a simple, straight black line. I choose "line tool" and have the weight set at one pixel, then hold down the shift key as I draw my line to make it straight. Problem is that the lines are coming out at different thicknesses and I can't figure out what variable is responsible for that - they should all be only 1 pixel wide but about every 5 lines or so, I'll get one that is 2 or 3 pixels. I'm trying to draw a "grid" that looks like a strip-hardwood flooring pattern and the unequal line thickness has me perplexed. Also, is there perhaps somewhere I could download a pattern fill that looks like a hardwood floor, rather than trying to draw my own? I'm not worried about color - i just want the line pattern.
Thanks,
Ez

I started a new image and the problem with the uneven lines went away. May have just been a glitch.

Ez

Could also have been a simple screen resolution problem where the lines appear to be thicker on the screen than they actually are.
If it happens again, try zooming in on your line to see if that is the case.

yeah photoshop doesn't really antialias at odd zoom levels, so stuff looks a little messed up.