Hi, I've been working on DIG-labeling northern blotting for a while, but recently i get some troubles regard to the background.

As the picture below, i keep having these non-specific bands in my background. I'm not even sure whether it is background.

I'm using 75% of Formamide of hybridization buffer and DIG-lableing RNA probe. This probe is specific to positive strand of virural RNA. At the same position, there are also some traces in the negative strand. These are the same samples which hybridized with positive and negative strand each.

Thanks a lot.