It very well could just be your printer/ink/paper combination. There are some printers that will print blacks with a brown/bronze tint. I haven't witnessed this myself being that I don't print B&W much, but I believe this is what they call "bronzing".
Printers/inks will also bronze on certain paper. Here's a link to a printer that printed just fine on certain paper with no bronzing effect, but on other papers, noticeable bronzing occurred.
http://grandwebsite.com/HP-B9180-Review.htm
When I was researching wide format printers for work, HP's latest 44" Z3100 printer added a "gloss enhancer" that effectively got rid of all bronzing no matter what the media is. But this comes at a price tag of over $5000.
Point is, I'd also look at your printer/ink/paper combo.