Have you checked the tray on the top of the motor/compressor round the rear of the appliance?
These trays fill up with water sometimes and any waste that is in the water rots and causes the smell
When you turn the appliance around so that you are looking at the rear of the appliance, the compressor is at the bottom and is a large domed black metal object in most cases. The tray you are looking for is on the top of that compressor.
Let me know what you find.
Let me know what you find so that we can take this a little further... If I am not about, leave me a message.