A blower motor issue can contribute to the noise in a furnace. When the blower motor malfunctions, it may cause the fan to spin unevenly or become imbalanced. This can result in vibrations and rattling noises when the furnace starts up. Additionally, a faulty blower motor may produce a loud humming sound or squealing noise. It is important to have a professional inspect and repair any issues with the blower motor to ensure the proper functioning of your furnace.