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I have had some luck spraying WD40 on the steering column universal joint that is directly beneath the brake booster in the engine compartment. Easy to see if you lean over the brake booster and look below it, close to the firewall. It is a silver U-joint on the steering column. It is a real b*tch to get to from above, but luckily the WD40 sprays pretty far. I can get a small can of WD40 beneath the brake booster somewhat and then let it fly, soaking the U-joint. The noise will go away, but will return after a few days. I would rather spray it white lithium grease, but that does not travel nearly as far as the WD40, so my attempts have failed thus far. I am confident that U-joint is the culprit, as the noise completely disappears when I douse it with WD40, but it needs some heavier lubricant to really soak in and be a more permanent solution. I will keep trying to get at it. Maybe better access from underneath the car?