Try getting an old coke bottle(plastic) or even a short broom stick handle. If you have a couple extra bucks a mechanics stethoscope is a good investment. Either way take these "tools" and place them in various areas where you think the sound might be coming from and then put the other end on your ear and listen for the sound. Keeping clear of the moving parts. Move it around till the sound gets more intense. That will help at least point you in the right direction.
"If you ain't moving fast enough your costing me money and if your costing me money you ain't moving fast enough." -"The Machine"-