Squawking noise on and off

[His Dudeness]

Do you lube the chain regularly? If the chain is dry lube it and see if that improves things. Assuming the chain is all good so it's lubed, the tension is right, it's aligned properly, there's no tight spots, the sprockets are good, the front sprocket nut is tight. The next thing to check is the bearings in the rear wheel. There's two in the rear wheel and one in the rear sprocket carrier as Jamieg285 said. To check them properly you have to take the rear wheel off, put your fingers in the bearings and spin the wheel and feel for binding or rough spots in the bearings. The bearing for the front sprocket is inside the engine. It's the bearing for the output shaft of the gearbox. It would be very bad if the problem was that bearing. You have to strip the whole engine to get to it but most likely it's not that bearing that is the problem. Generally they good bad from over tightening the chain not from letting the chain go too slack