Today I put the car up and inspected the flex discs: They look like new. I also inspected the linkage from the shift lever to the transmission as Chas H suggested: It was a little off, I set it to the book. The clicking sound is still there when the transmission is cold. After driving a little, like one mile, and going back into my driveway, or any sloped road, the sound has disappeared. I'm afraid M.B.Doc is right!