Can we disable Approval email notifications for Sales Orders only?

1) Although we do not have SO Approval rules defined, the Sales Orders are getting stuck in 'Approval Pending' status, sometimes for indefinite period of time. In most cases, when we submit the SO, it changes to Approval Pending, and within few seconds, it moves to Processing status. But in some cases, sales orders get stuck in Approval Pending status until someone manually progresses it. Users have to manually intervene. This is incorrect because, we do not have any approval process, defined in the system for this Business Unit. So, ideally SOs must never change to Approval Pending status. However