Is there any rattling or is it a pure whirring noise? I ask because there are multiple little flaps in the housing around the fan itself that can get broken off and ingested into the fan and cause a lot of racket.
Another cause of racket is simply a build-up of leaves and debris between the fan and the radiator. About the only way to fix either of these problems is to remove the fan itself and clean everything out.
When I did mine (it had ingested a couple of its own flaps and sounded terrible), it took me about 4 hours, but I work slowly. I followed my Bentley manual's instructions, which required removing the fog lights, headlight trim strips, the bumper, the headlights, and then (finally) the electronic fan itself.
I am 99% certain the fan pushes (or should be pushing) the air front-to-rear.
There is also a nice write-up somewhere (bmwtips.com?) providing tips on troubleshooting that pusher fan.
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2006 Honda Odyssey EXL-RES
2006 Honda Accord V6 EX-L Sedan
1999 BMW 540i 6-Speed (Sold to M3UOND on 9/21/06)
1991 Honda Civic Si - Occasional Beater