I have been putting a K75 RT back together over the last month or so and finally got to the place where I can ride it. I noticed that when starting off in first I had a fairly good rattle and clatter. I was not expecting that after a new clutch and good pressure plate (the plate just need to be scuffed with a sanding pad) and a total spline lube.No FD play to speak of and all the drive line stuff seemed ok, u-joints etc..
While getting ready to go for another ride I rolled the bike off the center stand and my wife who was outside with me said: Is the bike supposed to bounce like that??.
I had not noticed that the rear shock was really weak. I replaced the 20 year old original shock with a new 412 from Progressive Shocks and no more noise and the bike handles like brand new(I changed the fork oil also).

yay ...at least you didnt have to go back in to "elbow deep" to correct the issue chris ....congrats

Believe me that was constantly on my mind as I was monkeying around with it trying to figure out what was wrong, my first thought was what did I do wrong because I had been in the trans replacing the input shaft for worn splines.