Usually things made of heavy plastics have a date at which the plastic starts to break down. I first noticed this on child booster seats - there is a date stamped on them. I would assume that aerobic steps would have a certain lifespan, and at some point would lose their 'shock absorption' or strength or something. The reason I ask is - I bought my step on ebay. I knew it was used, but when I received it, it looks like it was used in a health club for MANY years, then left sitting in the sun for a few seasons. Also, the black rubbery ridges on the top are kinda worn out. I had a brand new step several years ago, and it didn't rattle when I used it, but this used step is noisy. Maybe I am just looking for an excuse to buy a shiny-and-new step. Any thoughts on this issue? Thanks!