Look lower on the exhaust pipe, about where it is below the passenger's seat. If your transmission is leaking fluid, it ends up there and can give you some smoke. You will see a stain on the pipe where the fluid has spattered and cooked onto the hot pipe. Trans fluid will also give white smoke. Mine has started dripping recently and it gave me some smoke once. Not clouds, but enough to make me pull out of the bumper to bumper traffic I was sitting in and stick my head under the car. It still drips there, but a quick trip to the car wash and a spray of the wash hose cleaned the crud off and no more smoke.

Good luck!

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1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)