I own several M4700 and M4800 Precision workstations, each with the unbelievable fan noise issue. I went thru all of the "checklist" of fixes, especially: Uninstalled Dell Bluetooth drivers, and Disabled Windows Search. Still, the fan would come on whenever a new webpage was browsed or new work started, seemingly related to showing me a window. But, downloading "Throttlestop," unzipping, (including a detour to install the Visual 2013 C++ redistributables) clicking "Turn On" and clicking "Chipset Modulation" and clicking the arrow "down" one notch, to 87.5%, has solved MOST OF the problem. Peace and quiet for normal stuff involving Intel for graphics. For intensive graphics card use, the fan is still always on. Note the "fix" cost me 0.1 in the Windows RAM performance assessment. I believe the fan issue is ultra-transient temperature spikes triggering the fan's control even when the spike lasts a microsecond or so. 'Get bent', Dell and Intel, for not solving this yourselves in the BIOS.
What bios-version are you running? I recently bought a used M4800 and I had the same issue. The fan could start for no apparent reason and make a lot of noise. Regulating extremely unevenly at low temperatures sometimes.
I'm running Ubuntu 18.04, but I tested it out with Windows 10 also and it made no difference. Last night I upgraded the bios from A06 to A25 and there was a substantial difference. Something changed, and I am hopeful that it resolved the issue for me at least. I guess time will tell.