: I have an 82 p-200.when I "bounce" up and down on the seat,the rear shock makes a really gross noise,

Well then don't bounce up and down on the seat.:-)

Seriously though, Its a good chance that the shock is totally screwed, replace it with a Sebac (adjustable), they last longer. If you replace it with another used one this problem will happen again way sooner than you would expect.
Another thing, be sure that the large engine bolt is greased and able to allow the engine to swing with no resistance.
Also Woody's suggestion would be wise to check out the frame for any cracks around the shock support.
Good luch,
Dennis
Scooter MD