On mine, simply remove the glove box by popping the plastic "rivets" around the inside edges and I get full access to the fan. As it is a sucker, rather than a pusher, perhaps it has ingested something that makes it squeal. You might look down the throat to see if that has happened and, in any case, I'd shoot a shot of something like WD-40 into the impeller area to see if it helped reduce the noise.

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles