The water heater makes Noise during heating, Very unpleasant and feels that it may malfunction, Understood that it is due to scaling. The scaling do happen in other water heaters but not happy with the noise it comes during heating, as per the Bangalore service in charge Mr Bharath 9886309501, it is known issue and they reported to R&D, But no resolution.If it is know issue, it should be mentioned, I world not have bought the product. At least it should be mentioned what should be TDS level the water heater supports without noise. My opinion has completely changed about the AO Smith. No more "fit it forget it" As It make noise. To clean the noise. we need to call service which is again paid service(Rs. 400/-) as it is scaling removal is not a part of heater. I think if AO smith really wish to have good product.Please resolve the issue of noise. I am disappointed with my three nos of HSE-SDS 025 purchases. Do not recommend if you wish quite water heater!