I know of a text in which it says the body is a burden, feelings are a burden, what are called the five aggregates are burdens. Here the idea is they become a burden if we identify ourselves with them. A burden is something that we have to carry. So to put down the burden that we are carrying we have to learn not to identify with these five aggregates. Then they do not become a burden because, as you rightly said, in the case of an arahant, an enlightened person, this is how he or she sees the five aggregates. To put it in another way, these five aggregates when we are identifying ourselves with them become a source of suffering, and if we can let go of identification with these five aggregates, then the burden goes away and there is no suffering.