ours did that when we first got it installed, but it was so faint it was hard to notice and eventually worked its self out.
Have they replaced the 2ND BTR, IBT Belt, Pressure roll?
Have you setup the Secondary Transfer Voltage Adjustment in the Custom Paper Settings in the Amin Mode?
For about a month now I have been getting strange areas on lighter stocks 80# text or less, but not on cover stock. The technicians can't seems to figure it out and have replaced multiple parts and fusers. Has anyone else come across this issue? Its shows up on all colors. Could this just be a humidity issue?? See Pictures.