Oracle recommend using the DBMS_AUDIT_MGMT package to move the sys.aud$ table from the System Tablespace to another.

I created a new Tablespace called AUDIT_DATA and then ran this procedure.

SQL> begin
  2  DBMS_AUDIT_MGMT.SET_AUDIT_TRAIL_LOCATION(
  3  audit_trail_type => DBMS_AUDIT_MGMT.AUDIT_TRAIL_DB_STD,
  4  audit_trail_location_value => 'AUDIT_DATA');
  5  end;
  6  /

PL/SQL procedure successfully completed.

it's simple and it works... nice