Normal. My Volvo sounds like a jet engine, really howls (so does the turbo).
You should be getting the sound on startup for a few seconds, maybe longer.
As the temp of the air off the rad changes, the fan will go on and off -- when off, the fan turns arou 800 rpm, more less independent of engine speed. When it's on, it will turn up to 3000 rpm or so, directly dependent upon engine speed.
It will come and goe in traffic, even on the highway if you are in traffic and speeding up and slowing down a lot -- the Volvo used to come on and off in Cincinnatti when I drove through there -- the combination of heavy acceleration and intermittant slowing down would kick it on, AC or not.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!