I have a 04 F150, everytime I use the wipers I feel a thump in the brake pedal when im holding down the brake. Is this normal?

 

I own an '05 and don't have this problem.

My guess is that what you are feeling is resonating from the firewall / instrument panel where the wiper motor is mounted. Either the motor or linkage may be binding or have excess play in it. This was common on older vehicles after running them for many years and things wore out. Not to say yours is worn but you may have similar circumstances.