Yep, best thing to sort that is to run it empty on the hottest wash. Before starting the wash pour a small bottle of white vinegar into the drum. Let it progress through the cycle. Do the same again, this time putting some of your detergent in the drawer, or just use some soda crystals instead. Again, hottest wash with nothing in it.
After that, make sure you leave the door of it open so the drum can dry out. Same goes for when you've just washed clothes, leave the washer door open as long as possible so it dries out. You should find that the smell goes away.