Has it always sounded like this or have you just recently noticed it?
Is this noise still there for about 30secs after you've switched your car off after a drive?
S13's in the US are 240SX's.
200SX's over there are B14/B15......similar **** to our Pulsars.
They can also be known as the classic 200SX which were the S10, S110 and S12's.