Port 1433 is commonly used by Microsoft SQL Server, which is a database management system. A spike in traffic on this port between two IP addresses on opposite sides of a WAN connection could indicate a database replication process, which is a way of copying and distributing data from one database server to another. This could be a legitimate activity performed by an administrator, but it should be communicated to the security operations center (SOC) to avoid confusion and false alarms.
References: CompTIA CySA+ CS0-003 Certification Study Guide, Chapter 3: Security Operations, page 107; CompTIA CySA+ Study Guide: Exam CS0-003, 3rd Edition, Chapter 4: Security Operations, page 153.