Hi John,
If you already got this, please disregard this one as my sent box says I didn't send it.
I bought a 1655 recently knowing that it has a &quot;clunk&quot; in the trans. It clanks about 4-5 times every tire rev. When I go downhill, the clunking stops, and then starts again with a little higher pitch as the trans slows the tractor. 
I'm not asking for a dianostic with this little info, but wondering where You would start looking. Pull the seat/hydrolics and start at the top or try to see something from the side like the brake area or axles.
Since the noise stays evenly spaced with the drive tires, I'm think bevel gear or pinions......?

Thanx for any input, Larry Coltrin