ford focus tddi - whines through start operation - micksta

i bought this car 2 months ago and it ws fine apart from a slipping clutch, i had used abit of bio diesel for couple of days then it got harder to start so i stopped using the bio and went back to normal diesel. it is still abit hard to start and kinda whines throught the start operation but once started its fine. i think i may have clogged the glow plugs or something can they be cleaned or should i just replace them?