trolling motor gurus need some help

2006 minn kota maxxum 80. i was out and my motor started making a knocking noise like im hitting a tullie but there's nothing there .then my motor quites. when i push the pedal it clicks and the lite lites up but no go i  tapped the housing and it kicks back. in it seems to knock more at 40 and below at higher speeds it will knock a bit then balance out i stopped  took off the prop and it knocks without the prop so its not the prop. then i pulled the houseing and all the connections are fine  it seems to kick back on whenever i slap the houseing weird the connections are fine im stumped anyone got an idea ?