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Have you recently moved the oven racks or used the convection fan?
Sometimes when shifting around the racks it can cause the vibration alone.
if not, then I would open the oven door and pull the racks forward about an inch then try it again.
sometimes when the oven racks are pushed back too far against the oven cavity they can rattle or vibrate when the oven is on giving you the noise you are referring too.
If that doesn't help then the convection fan itself could be the problem. Sometimes when the convection fan motor is going bad the shaft and main bearing of the fan will become noisy when it is in use. But this should only be noisy when the convection fan is in use.
Check those things and get back to me here and let me know and I will help you more.