Safety first: Disconnect mains power and allow the oven to cool before inspecting fans.

Steps to diagnose and fix:

Identify noise source: Run the oven briefly (if safe) to determine whether the noise comes from the rear (convection fan) or top/rear (cooling fan). Then disconnect power.
Inspect convection fan: Remove the inner rear panel and check that the fan blade is securely fastened to the motor shaft. Tighten the retaining nut if loose.
Check for debris: Remove any loose screws, foil, or food debris caught in the fan blades or housing.
Test motor bearings: Spin the fan by hand. Roughness, wobble, or play in the shaft indicates worn bearings. Replace the OBH Nordica-compatible convection fan motor assembly.
Inspect cooling fan: Access the top or rear cooling fan and ensure it is firmly mounted and free of obstructions. Tighten mounting screws and reposition any contacting panels.
Test: Reassemble, restore power, and run the oven to confirm that the noise is eliminated.

Oven makes loud rattling or grinding noises during operation, especially when the fan is running.

Possible Causes