I have an old MC 3000. It made a horrible whining sound about 20 seconds after I started up so I did this. I took off every cover (one at a time and thoroughly cleaned everywhere).
Nothing. It still happened. So this time I took off every cover the same time and ran the machine listening for where the shrieking noise came from. It was from the front left so I reached a q-tip way up and in there by holding one w/ tweezers and got a big old dust bunny (moose) out and oiled all over in there too.
Wa-la. My machine has been good for beyond two years since that episode. It was in front top (but under needle plate). Don't know if this will help you.
Anne Marie D.