[Protein-analysis] silver stained band at the running front

[Monica Fazzini]

Hi,
I've been running some of my samples on 4-20% SDS_PAGE, and I've noticed that when I silver stain, a band appeard at the running front. This band doesn't appear in lane without sample just loaded with Loading buffer. In addition, it stains more greyish than the rest of the proteins that are more brownish. Any suggestion about the nature of the band?
Thank you,
Monica