Herringbone patterns are evenly spaced wavy lines that appear on your TV screen. They are usually caused by having a second signal located inside the frequency band of the signal you want to receive. Sometimes the lines are so close together that it appears to be snow, so look carefully. To cure this problem, you first must determine if the problem is an extra signal and where the extra signal comes from.
Ant channels are ok.
First, try changing the modulator channel number. If the herringbones still persist, then the problem may be a mistuned modulator, rather than an extra signal. Consult the manual for instructions on changing cable standards. You will have to filter out the offending signal. This is a poor filter, suitable for troubleshooting only.