I'm not sure about your Janome 8900 but when my Janome 6500 clacks it is the bobbin jumping and rattling. Under the bobbin case there is a little hole with an oil wick (it isn't lint!) that sometimes dries out and needs a drop of oil. No where in the manual does it tell you this and my dealer didn't tell me either! I found out about it finally on the Janome 6500/6600 Yahoo group. I just give it a little oil when it starts to clack and that has saved me from repair bills.