if you have soffit vents you should have a ridge vent and then,,no you don't necessarily need the gable vents on the ends. That being said noise doesn't flow like air so I don't think the source of your noise is through the vents. Do you have bat insulation in the attic? I'd suggest that to reduce noise transmission from the attic space. it could be wind noise coming through the structure. Without actually experiencing the situation first-hand it's difficult to propose remedies.

good luck