My '89 has a rattling noise from the transaxle. It has 145000 miles on it and works great. No problems in operation.

Through a little research I have found that they used a chain and gears in the transaxle. Could this be the noise I am hearing? It sounds like a used timing chain and gears, but it is heard on the drivers side (transaxle area).

If so, how hard is it to change and what are the part numbers needed?

Do you hear this noise ALL the time. It'* possible that what you might be hearing is the rattlling of a loose catalytic coverter shield. But that'* just the optimist in me.