my aux fan rubs the cage when it first kicks in, making a scratchy loud noise. within 30 secs or so, it goes away. not sure why. maybe the cage got warm and buckled forward, causing just enough clearance.

i've looked into it but not sure what to do or fix. from what i can see, the electric motor is mounted to the radiator bracket, and the radiator bracket gets mounted to the body. i'm speculating that the radiator mount needs to be shimmied just a tad to make the tiny additional clearance needed but not sure.

any suggestion?

are you sure?, do you only hear the noise when you have the a/c on, a faulty a/c compressor can sound like a faulty fan blade hitting the shroud.

I had a similar problem on a benz and it was a collapsed engine mount, replaced and everything was back to normal. The noise was constant though and didnt go away after 30 seconds as you describe. I just read you said aux fan, my problem was with the mechanical fan, not sure if thats what your problem is but a good tip either way if your mechanical fan is touching the shroud.

are you sure?, do you only hear the noise when you have the a/c on, a faulty a/c compressor can sound like a faulty fan blade hitting the shroud.

yep. i hear the noise once a while, not very often, even without the a/c on. for example, after a stop and go driving, i went to a drive-through atm, took a little longer to dep check, there it went, crackling noise, then it was 'tapering' off after less than a minute. what i mean by tapering off is that the 'rubbing' sound gets less rubbing, and it goes away and i check the aux fan is still on, smooth sound, so it's not the bearing. btw, the front edges of the blades of the fan seem to rub the plastic cage cover. i'm so tempted to just snip the four tabs where the allen screws hold the flimsy cage. it looks as though it's designed by lawyers trying to avoid lawsuit.

here's a diagram of the aux fan:
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item 6 and 7 rub item 5.

EDIT: #6 and #7 are too flimsy, IMO, but i'm afraid if i swap it, same flimsiness, it may not solve the problem. leaning towards fan misalignment issue, but not sure how to address it, until i tear it up, hopefully tomorrow.

There is a another shroud that sometimes rubs against the aux fan - it sits on top of it, you can see it when you take the front end apart to replace it. I had the same rubbing issues. I think it's the one that bolts or snaps onto the top of the radiator in three places, you can see it when you open the hood.

Anyway, I had to take mine back apart and put a spacer in it. I think I read somewhere that this shroud can become warped over time with heat.

My fan rubs too, but its because the blade sits loose on the fan motor shaft & rubs on the shroud. You have to replace the whole unit so I'll just wait till it gets anoying.

There is a another shroud that sometimes rubs against the aux fan - it sits on top of it, you can see it when you take the front end apart to replace it. I had the same rubbing issues. I think it's the one that bolts or snaps onto the top of the radiator in three places, you can see it when you open the hood.

Anyway, I had to take mine back apart and put a spacer in it. I think I read somewhere that this shroud can become warped over time with heat.

you're absolutely right. mine is warped beyond reshaping. where did you put the spacer?

Depending on how it's warped, you can put it in different places. When you take the bumper off, you will see where the mounting bolts are. If you are going to go through all of that trouble, you might as well order a new part.

http://www.bmwtips.com/tipsntricks/auxfan/auxfan.htm

See the black thing with two square holes that goes over the fan assembly? That's the part that warped on mine. I think I put the spacer in down near one of those bolts at the bottom. I also replaced the three snap-on things at the top with bolts and then tightened them down while pulling out on the black thing.

Like I said, if that's your problem, it's probably better to just replace it.