You should move the database Audit Trail to a Different Tablespace

You may want to move the database audit trail tables to a different tablespace if the SYSTEM tablespace is too busy

Run the DBMS_AUDIT_MGMT.SET_AUDIT_TRAIL_LOCATION PL/SQL procedure to specify the name of the destination tablespace and move it to that tablespace.

BEGIN
 DBMS_AUDIT_MGMT.SET_AUDIT_TRAIL_LOCATION(
  AUDIT_TRAIL_TYPE            => DBMS_AUDIT_MGMT.AUDIT_TRAIL_AUD_STD, 
  AUDIT_TRAIL_LOCATION_VALUE  => 'AUD_AUX');
END;