Can you Help me figure out what this noise is

Hi I have a 2003 Dodge Intrepid.
Since I have had the car about 2
years now it sounded like my muffler
was not secure. I havent taken it in
yet, but i wanted to try and figure out
what the problem could be and
maybe save a lil miney on labor. one
day I noticed when I drive straight I
feel a tapping on the floor ( front
driver side area)and it sounds like a
repetitive clunking sound. Kind of like
when you were a kid you would put a
card into the spokes of your bike but
the noise is much louder and of
course it doesn't sound like a card
but it's repetitive like that. I have
noticed when driving at high speeds
it's not as noticeable, It will stop if I
push the brake halfway in but as
soon as I let off the brake it starts up
again it's getting louder by the day
and it feel like my whole wheel is
going to fall off or itll end up causing
an accident. I have kids so im extra
nervouse please can you guys help
me figure this out so I know where to
start.
Thank you...