windy roar that comes and goes (560SL)

[tahodgson]

Have an '87 560SL.

From time to time, there comes (seemingly) from under the engine compartment a windy, almost hollow-sounding roar...as if a strong fan were kicking in...the noise almost always abates when I ease up on the gas, but I can't correlate its changes with engine vacuum or RPM.

Does this engine have an electric fan that kicks in?

It's my first Mercedes, and I have no points of reference.

Any thoughts would be appreciated, as always.

~Tom