Whenever the car changes attitude suddenly (speed up/slow down in parking lot, sharp turn, going over a speed bump) I hear a pronounced whirring noise, kind of a RRRRRRNH like the sound of the engine revving. It corresponds with hitting the bottom of a dip or clunking over a speed bump most of all.
I suspect the fan or fan clutch because I hear a quieter version of the sound the whole time the engine's on. It's like the fan is off balance or something.

How can I test/verify this? Also, I've read something about refillig the fan clutch with fluid of the appropriate viscosity, is that possible? I really can't afford a new fan clutch right now, especially in light of other things Ilse needs.

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)