Intake can significantly contribute to noise .. since you mentioned it's not the stock carb, it probably doesn't have the stock airbox and filter either. Intake roar is second only to exhaust noise in an otherwise healthy engine.. Mechanical noise is next in line.
To check intake roar just put your hand or a rag over the carb intake. If the thing gets real quiet all of a sudden, that may be one place to devote some effort.