My double ovens make a horrible noise when working. A noise started several months ago when the ovens were pre-heating. Now the noise is extremely loud and starts when I turn the ovens (one or both) on and does not stop until they have been turned off and cooled down.

Look at these: https://dl.dropbox.com/u/8010163/Whi..._Gas_Ovens.zip
I think you have a motor that had bearings and needs to be replaced. You need to open the oven doors and look for the name plate that has the model number and give us that along with the name of the oven. Then everyone can find the right manual.