The drum on my Zanussi washing machine is sticking slightly. ?

The drum turns but not freely, feels like it has something stuck behind it. How do you get behind the drum to clear what is catching? I suspect a small sock has got caught somewhere. It doesn't seem to have impaired the wash but spinning is no where near as good as it was, clothes come out with a lot of water still in, not dripping but very heavy. It's a zanussi aquacycle XC, FLE 1416W hope some one out there can help... thanks