98 Grand Caravan

I have a 98 Grand Caravan with a 3.3L auto and air. The vehicle has 230,000
Km's and runs great, no major problems in the 6 months that I've had it. I
have noticed that with the radio off and the windows down I can hear a
clicking sound (maybe from the tranny) when I slow down to a stop. Seems to
me that I've heard it before in other GC's but not too sure. The van drives
and runs great and i'm just hoping that this is not a sign of impending
failure and that it's normal. Thank in advance for any help.