Disc brakes on new leisure bike sounds like toilet flushing

I recommending cleaning the rotors and pads. Not sure why you didn't start with that if you have been googling in your research.
 
Yes, but the water sloshing noise started before it was even taken to the shop. It was noiseless for 20km, then got really bad.

It sounds to me like something got imbedded in the pads and when you actuate the brake it grinds against the rotor. I would clean the rotor and pull the pads and clean them also. You could even swap the front for the rear and see if it grinds in the front; then you would know it is a pad problem and not an adjustment/alignment issue.
 
All I hope for is someone to Recognize the Sound, to identify the sound, its origin, its cause. I wouldn’t be here if I had not already talked to bike shops and the company, presented them with audio, and did a very thorough search of YouTube. So far, no one is saying “I know that sound!” which is to me, incredible. I cannot be the only person to have ever heard this noise on an Ebike with disc brakes. I have heard solutions of ‘water in the pipes‘ (it’s not), align the pads (they are aligned) or simply ‘return it‘. It’s all guesswork so far. So I’m hoping someone here knows more than the company itself or a professional Ebike repair shop. I don’t know where else I can go for answers. All I can hope for is that I can get a refund if problem is not solved.
 
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Update from bike shop. They sanded the pads, cleaned the rotor, checked for anything loose, then told me it was fixed. I tested it and it‘s exactly the same. Either it was quiet for the few minutes they tested it or they have no ears. Next step: they will replace the pads completely. If this does not work, I have no idea.
 
Replaced front and back brake pads. They told me these were infected. (tektro) From a brand new bike with 20 Km on it! Did they come like this from the factory? The front ones were starting to make minor scuba noises as well, so got those replaced too. First photo is rear pads. (really bad noise) Second photo is front pads. (minor noise).

Noise problem solved. Cost so far for brake pad alignment plus new pads = $130 and six trips to bike shops. Let’s see if Rize will pay for this. I don’t see why I should.

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My Spark City Tektro rear brake sounds like grinding on concrete, a very coarse rumbling sound. But I didn't bed in the pads to begin with. I blame that in the absence of a better reason.

After carefully cleaning the discs with alcohol, sandpapering and cleaning and burning the pads with alcohol, and then bedding them in by going downhill and applying the brakes hard but not locked until the bike is slowed down a lot, repeated again and again, the noise was gone. But with use, the sound did return when brakes are applied hard.

As a complete newb to bicycle disc brakes/hydraulic brakes I didn't and don't have enough experience to know more.

It doesn't bother me much because I have 3700km city stop and go riding and they do work well to stop the bike
 
Just a virtualknow nothing on the subject, guessing.
Was there sufficient brake fluid in the rear line? Did the bike shop add fluid? It seems as if it's the disc making the sound due to a vibration. Also the pad looks like it was pushing on one spot. Could it have been bending the disc when pressure was applied?
 
Are they semi metallic or organic pads? I have had to have pads changed to organic to eliminate horrible grinding noise on a bike. Once the organics were on the noise was gone.
 
Just a virtualknow nothing on the subject, guessing.
Was there sufficient brake fluid in the rear line? Did the bike shop add fluid? It seems as if it's the disc making the sound due to a vibration. Also the pad looks like it was pushing on one spot. Could it have been bending the disc when pressure was applied?

they did not add fluid or check fluid. The disc was straight.
 
Are they semi metallic or organic pads? I have had to have pads changed to organic to eliminate horrible grinding noise on a bike. Once the organics were on the noise was gone.

these are semi metallic. Jagwire deore. Let’s see how long they stay quiet.
 
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Now my Rize rx pro is making the same brake noises. Took a bit longer to kick in. Looks like Tektro pads are crap. The leisure with new pads did 35 km today and are still quiet. Looks like I will have to replace the rx pro pads as well.
 
Now my Rize rx pro is making the same brake noises. Took a bit longer to kick in. Looks like Tektro pads are crap. The leisure with new pads did 35 km today and are still quiet. Looks like I will have to replace the rx pro pads as well.
What Rize has given you is the new Tektro "Theramin" brakes that just came out.
 
I need to buy replacement pads. Any recommendations? Stick with semi metallic? Brand? Can‘ t seem to find anything on Amazon that doesn’t take 2 months to arrive. I can buy jagwire pads from the bike shop but they are $30 a pair before tax.
 
Find a steep hill. Try bedding in the pads really good. You got nothing to lose, you are going to replace them anyways.
Check to see if the brake disc is glazed.
 
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