You have a bad fan bearing bracket (what the fan clutch attaches to). You can't see it from the outside but once you get the bracket off you'll see the ball bearings literally falling out from the inside. The bearing typically collapses around 150k - 170k miles and the symptoms you describe fit it to a tee.

It's not that tough of a job but the part itself is kind've pricey. (~$160) Look up fan clutch bearing bracket.

Good Luck

__________________
-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi