I have a 2003 ls170 1300hrs there is a ratchet, clicking sound coming from both sides chains are adjusted properly. You can go into a pile of dirt and spin all for tires no noise. If you jack up one side with machine off and hand spin tires you can hear noise if you wait 15mins and spin tires noise gone.
Are you confident it’s both sides? Park brake isn’t stuck partially or anything? When the drive motors go bad on these, they make a horrid chain skipping type noise when cold. If you go full speed when machines cold, and pull back sticks immediately, it should of course stop. If it click and clacks like chain and sprocket skipping, your drive motors are going bad. Never seen both happen at 1300 hours. Although those old green LED displays went bad often and those hours are commonly wrong on those. Maybe you have the orange backlit display though. Spinning over the tires by hand also makes me think drive motor, it should be awfully tough to do that by hand.
No park brake on it anymore I swapped out used pumps and drive motors and does exactly same thing. If you go full travel forward no noise soon as you go in reverse fast horrible noise sometimes sounds like chain but it’s not the chains
Does it go away/get better when machine warms up?
I would say gets worse better when cold