If you notice your machine is getting noisy. Sounds like loose metal clanging and you generally keep your machine clean,
TRY OILING IT!
I changed a bobbin on Ms. Midge yesterday and in the process tried to diagnose the noise I keep hearing. Usually, I only hear the tinging when the bobbin thread is low but this was happening without a bobbin altogether.
So, I thought, what the heck, I'll oil down there and see what that does. HOLY CRAP... okay, I said the "S" word. NO noise.
I started sewing again and who knew, I actually have a quiet Ms. Midge. She's only been loud b/c I haven't been paying attention.
So yea, oil your damn machines.