Matt, my brothers/mine has this exact problem, I thought it was because the chain was worn out, but I've just put a new chain on to sell it and it's worse! I've knicked the tensioner I had on my Echo and used that, which is working for now. I could almost get a link out of the chain, but it woul be about 3mm too short if I did. PM me for helpies if you want, or MSN. I'm getting pics of it tonight to add to the for sale topic, so You can have a look at that for an idea of how to sort it.