Knocking and grinding sound from hub motor?

I have had quite a loud knocking sound coming from my girlfriends rear wheel which speeds up and slows down as the wheel rotates faster and slower. It started to turn into a grinding kind of sound and became noticeable louder so the insides of the hub were replaced but the old hub casing was left the same. The same knocking sound was immediately apparent as I left the store so I am back to square one. Anyone have any idea's please as I am clueless and the shop I got the bike from seems pretty unknowledgeable also. Thanks.

I have had quite a loud knocking sound coming from my girlfriends rear wheel which speeds up and slows down as the wheel rotates faster and slower. It started to turn into a grinding kind of sound and became noticeable louder so the insides of the hub were replaced but the old hub casing was left the same. The same knocking sound was immediately apparent as I left the store so I am back to square one. Anyone have any idea's please as I am clueless and the shop I got the bike from seems pretty unknowledgeable also. Thanks.

 

A bad hall connection can cause these symptoms, check that it is all plugged in properly and clean and dry. It will most likely be a 5/6 wire plug where the controller goes. What bike is it?

It is a Westhill Terrain and has a Bafang 8fun motor. I just uploaded a video of the problem. Thank you for the reply.

 

https://btcloud.bt.com/web/app/share/invite/fEnxYNBe9P

It is a Westhill Terrain and has a Bafang 8fun motor. I just uploaded a video of the problem. Thank you for the reply.

 

https://btcloud.bt.com/web/app/share/invite/fEnxYNBe9P

Ok that does sound like something has broken that's rather loud. Still to rule it out check the connections as I find that to be odd with brand new innards. Is the hub casing dented or damaged in any way?

Not that I can tell, everything looks in perfect condition still. I think the sound was always there from the start but I thought it was just the spokes wearing in as it was so faint. I guess a spoke problem is out of the question now as it is so much louder. I am thinking the casing has to be the culprit as they did not just replace the entire hub like they promised. I have no proof they replaced the inside of the hub tbh. Thanks again.

Had a sound like that on my bike last week. Turned out to be a 'pimple' on the brake disc, had to file it off. Does the sound go away when brake is applied?

I thought exactly the same thing but the sound is still there while pulling on the rear brake whilst cycling. I have just checked over the spokes again and found some of them completely loose and wobbling around so hopefully I have found the problem. Thank you so much for your quick and helpful replies.

I thought exactly the same thing but the sound is still there while pulling on the rear brake whilst cycling. I have just checked over the spokes again and found some of them completely loose and wobbling around so hopefully I have found the problem. Thank you so much for your quick and helpful replies.

 

Aha yes I had that issue. They started breaking after that

If you can't do it yourself, take the wheel to a LBS who build wheels. They will be able to re-tension all the spokes correctly for you. Shouldn't cost more than £15-20.

I took the bikes back to Cycle King and they did re-tension the spokes but the wheels are still not true, you can see it clearly. I have my free 6 week service that came with the bike so I will ask them to do it properly then but as they do not have tension tools or a truing stand, I am not sure how well it will turn out. I might just have to go to Halfords as they claim to have all of the correct tools and I can even watch them at work. Sounds more promising.

Any decent independent LBS should be able to true your wheel for around £15. They aren't hard to find, they have the small shops with staff who know what they're doing. IMO, no truing stand, your in the butchers next door!

My truing stand is the bike upside down. Spoke key and a couple of cable ties is all you need. Tension tool is my ear, any that sound dull probably need attention. Really, it's easier than I thought, done a couple now.