I have a minkota trolling motor but have noticed that it is making a knoking noise. The more i speed up the more it makes the noise. Sounds like an under water chopper. I have replaced the prop and the metal pin. Any advice would really help. This noise kills my silent approach while im fishing shallow.

might be a bent shaft making the prop rub on one side, pull the prop and spin the shaft and see if its turning straight.

Just wondering how do you get a bent shaft?

Hitting a rock or the hard bottom of the lake could bend it. Hitting a stump could bend it.
Pull the prop, hit the power and see if you notice any woble in the shaft.

could be the shear pin is bent or its worn out the slot it fits into on the back of the prop , check for ecessive play it that area and inspect the slot for wear

could be the shear pin is bent or its worn out the slot it fits into on the back of the prop , check for ecessive play it that area and inspect the slot for wear, if thats fine remove the prop and spin if the noise is in the motor it could be a damaged magnet

Also check to see if there is any play in the prop shaft, if there is, the bushing and seal is worn out, and that could be what is making your noise. Boris Marine Electronics on Azle Ave. can fix it right up. They do real good work, I have had very good luck with them.

Try this. turn the prop clockwise and counter clockwise about 1/4 turn each way. You will probably hear a clack..clack..clack. If you do, You have a magnet that has come loose.

Thanks for the advice i will take a look at all these things.

I have one that the magnet has come loose in twice and it sounds bad when it happens. The first time I tried to fix it with JB-Weld and had to have the motor replaced because the thickness of the JB-Weld took up too much of the gap between the armature and the magnet. The second time I used superglue gel and so far so good.