Bearing noise can be a constant rumble at low speeds that seems to dissappear as air flow noise increases, covering up motor and bearing noise. You can still usually hear some motor noise. In a nexus it is a low non intrusive sound and in other fans it can be a higher pitched sound. This becomes the characteristic sound of the fan. Sometimes, bearing noise is noticeable when you tilt it from a vertical or horizontal plane.
At 1000rpm, in most fans I've listened to, it is hard to hear much bearing noise, especially inside the case. I have noticed on a pretty good fan a resonance at a certain frequency, but that noise is closer to a constant whine that disappears quickly as the speed changes.
It sounds like the noise you describe is very annoying and I don't think that is normal. So if its not a loose wire or something that comes in contact with the blades, it should be quiet fan without the kind of noise that you describe. Since you can't take it apart without loosing the waranty I would call seasonic and see if they can send you a replacement or the dealer unless it was newegg in which case they can't really help you other that to exhange it and charge a restocking fee. - FG
e8400, Corsair XMS2-5400, Asus 8400GS, Gigabyte EP45-UD3R, Chenbro SR209/Nexus 120, T-Balancer, Enhance ENP-5150GH 500W, Seagate 7200.7 160MB (Retired: XP-120, FSP530-60GNA, Antec SP2.0 500W, Antec SLK3000B)