Hi, I have replaced an existing thermostatic shower mixer with . Grohtherm 2000 Thermostatic shower mixer 1/2" | GROHE The house has an unvented cylinder and the pressure out of the shower outlets is 2.0 bar. However, when the shower is switched on with a low flow rate, there is a whirring / whinning type sound which I think is coming from behind the tiles directly behind the shower bar. This noise reduces when the flow is increased or is masked by the increased sound from the water coming out. The previous shower bar was similar to this one . Artisan Thermo Shower Valve & Fast Fit Connectors| Bristan And it did not have this noise problem. Could this be due to the higher minimum operating pressure of 1.0 bar for the Grohe as opposed to 0.1 bar for the Bristan ? I have two unit of the Grohe and they both have the same problems in different showers of the house, so I don't think it product fault.