what is the spring loaded contact mechanism under bottom cover?

Underneath the bottom cover on 2.8 GHz 15 in macbook pro there is a spring loaded, dual contact, mechanism located between the RAM and Battery. On the cover itself, there are machined circular contact points that seem to be for grounding the lower cover.

Do you know what these are for? As they are causing an awful creaking noise when slight pressure is applied to lower cover.

It make the machine sound broken. It seems that a lot of people are complaining about this noise on the web.