Question

Are sound waves a part of an electromagnetic spectrum?

Answer 1

No, they are not.

Explanation:

Sound waves need a material medium to propagate (for example, air, water, wood, etc.) while electro-magnetic waves (that forms the EM spectrum) do not need a material medium but they are a perturbation of the electro-magnetic field.
Also:
Sound waves are LONGITUDINAL waves:

Electro-magnetic waves are TRANSVERSE waves.