Heh, trade phones? j/k.
I've found that I've been disabling vibrate because I rarely notice it, it's not quite vibrat-ey enough for my tastes. I do agree that it's loud, however, more often than not I hear it rather than feel it.
Unfortunately there aren't any controls for vibration intensity. Some apps let you change the vibrate 'mode', either long pulses, several short pulses, or a combination, but it always seems to vibrate at the same intensity, which won't help the noise issue.
I'm kind of thinking the noise is being caused by the backplate bouncing, so maybe you can 'mod' it by adding in some kind of shock-absorbent material between the battery and the backplate, but it'd have to be pretty thin.