I did a quick google search and didn't find much besides another thread on TB where it was mentioned that Ashdown said that they use 2 variable speed fans in that amp to keep noise down. That seems to imply that they're always on. And no judgement is implied but the amp was obviously not designed to be a used as a quiet practice amp given the amount of power it's capable of. It was engineered to be a reliable, loud amplifier. If it was designed to play at much quiet volumes it would end up being a practice amp-cheaper, smaller, lighter, and lower powered thereby removing the need for the fan.
...I dont know if the amp normally makes this much fan noise.
THIS! Stop worrying about it! Certain amplifiers are designed to have a continuously operating fan. I don't know of any class d amps that don't. The fan in my '80's SVT sounds like a freakin turbine but it's normal as it turns out. The prior owner was so concerned by the noise that he bought a new fan for it that turned out to be just as loud as the original. Now I have an SVT and a spare fan!