Comp clicks on boot

My computer makes this loud clicking sound nearly everytime I turn it on.  It shows my hard drives and CD drive, prompts me to save changes, then boots normally.  What's going on?

There seems to be a problem, Anonymous.  With the boot drive plugged in, my computer doesn't read the 250.  If I plug in the 250 by itself, the computer only reads 137.  What do I do?

In before kill yourself, barrel roll, ect.