Yesterday, I got so fed up with the huge noise that the 32gb HP6600 was making, I tried to make it quieter. I changed something in the Bios data that I thought might help, but it didn't. I Googled, to no avail. I tried replacing one of the fans - that made it worse.
Eventually, I gave up and ordered another of the 8gb boxes for £60, like the one I already bought, which is almost silent.
That seems to have done the trick. The new machine hasn't arrived yet, and probably won't until next week, but somehow the 32gb box got wind of its impending replacement, and has gone silent, or nearly so.
So did I waste £60? I don't think so, it's a terrific bargain (there's still a lot more available from that vendor at that price, if you need a new computer) and I'll use it to replace another machine that I use as a terminal workstation. So it'll replace a machine running a Pentium 1 at 833 MHz, and 1/2 gb of memory, running Fedora 9 32 bit, with a machine running a Xeon 2.4 ghx and 8gb running Fedora 26 64 bit, and it'll run more quietly than the existing box.