Bernina deco noise

Question

I have a Bernina Deco 650 that sometimes makes a loud screeching noise that comes and goes when the machine is running. I cleaned under the plate and changed the needle. It still made the noise, so I took the needle out and ran the machine without the bobbin, spool thread and without a needle...still makes the noise. The book does not say where to oil it. Does it not need to be lubricated?