Yes there is a buildup of static because when you walked across the carpet the static cling from the carpet came to you because electricity and static are the same and static goes through water (all people are all made up from 70 percent water) so therefor it went to you then water can transfer static one place to another it traveled to metal and that therefor creates a shock using A and B particles like a magnet when they attract causing a buildup in the doorknob to shock you and going to person to person like a chain of electric static.
