My fiancee surprised me with the Minn Kota Endura Max 55 for my birthday coupled with a wonderful inflatable Sea Eagle boat for us to cruise around the Northern Montana lakes in. Lovely woman I have!

 

We take if for our first test drive and I have it hooked up to a 29 Deep Cycle Marine Battery to make sure I'm not bottle necking it's performance. Right off the bat we crank it up to speeds 3, 4, and 5 and the motor makes a pretty disturbing and loud abrasive humming/whining sound and appeared to be struggling. Thought maybe this was it just needing to be broke in (I'm an absolute noob with marine hardware.) We back trolled in reverse for a couple seconds and noticed it did this the worst on this speed. I'm guessing my motor isn't supposed to be doing this. It ran terribly and I have no idea what to do or look for. Anyone else have this issue?

Have you referenced your owner's manual? Did you install a breaker/fuse? I would check the prop first off and make sure everything looks good there including your prop nut and pin are installed correctly. Don't try to open up the motor in any way or you'll most likely void your warranty. All else fails, contact Minn Kota. 

Have you referenced your owner's manual? Did you install a breaker/fuse? I would check the prop first off and make sure everything looks good there including your prop nut and pin are installed correctly. Don't try to open up the motor in any way or you'll most likely void your warranty. All else fails, contact Minn Kota. 

this x2

 

It's normal for them to make a little noise, but from what you're describing it does not sound normal at all. 

Being new and unfamiliar with them, take the prop off and run it a few seconds and see if it still makes that same noise. If it does, see about returning it to where it was purchased, it's a bad motor. You don't have to have it in the water just to run if for several seconds, so you can check it at the house. If it runs nice and smooth with the prop off, make sure the prop was installed correctly. Make sure the shear pin is in that little hole on the prop shaft is even on both sides. Then make sure that recess in the back of the prop fits over the shear pin and the prop is all the way down on it. Put the nut on and try it again with the prop for a few seconds. Make sure the prop is clear of anything it might hit. Other than a low hum, if it's nice and smooth, try it again at the lake. If it does it again, then, take it back to the dealer.

Also, another bit of info, when you have it on or near max, don't think for a minute you are going to go cruising the lake for very long. Maybe 1 1/2 hours, and make sure you are not too far from the boat ramp after about an hour, until you have an idea how long it will run.

If you have a small volt meter, fully charged it should be approx. 12.8 volts, each 1/10 of a volt drop is approx. 10% battery. 11.8 volts is fully discharge and the motor will be just barely turning at that point, which is hard on the battery, so you should only take it down to about 12.0 volts.