Colour lines across the page (by 2 users)

Hello, sorry to bother you. I replaced the drum on my AL1100 but the printouts have horizontal coloured (the 4 toner colours)across the page (from edge to edge). They are randomly printed but on average 7 thick lines across the page. The lines have been encountered even before the drum was changed, in fact I thought it was the drum. The black toner is a little low but otherwise all is fine. Could you recommend something please? Thanks