WEBASTO Heat exchanger with heater fan MADERA 4D

Has anyone any idea how to mount this unit? And which pipe is flow and which return please?

I have just had a Webasto diesel (Evo5 Hydronic) water heater and Madera 4D fan (room fan heater) assembly installed in a motorhome. Both units work fine. My issue however, is the excessive fan noise experienced from the Madera unit, even on the lowest of the three speed options. It is most unacceptable just sitting in the vehicle, but it would be unbearable to "sleep with". Has anyone experienced a similar result and if so, can you suggest how to "fix it". My fan unit is mounted under the rear cabin seat and is less than 300mm from the "outlet" into the sitting area. 1/ Do I reposition the fan unit further away and run longer air hose lines to my outlets? 2/ Is it possible to reduce the excessive air volume (speed and mass) by way of a resistor, to maybe "quieten" the whole unit? The water heater, like any diesel furnace, is a little noisy on start-up, however it is most acceptable very quickly thereafter. It is the "matched" fan unit Webasto suggested, that is too noisy. Any thoughts and comments appreciated!