Regarding the ABS light, you can pull codes from the ABS computer. If it comes back as one of the relatively generic codes, try flushing a ton of brake fluid through the system. Mine came on a while back, and bleeding out the brakes while continuallly adding new fluid to the reservoir (about 16oz total) made it stay gone. Resetting the codes would ususally make it go away for a couple days, but it always came back before I flushed it out...
About the noise, Josh is describing the rush of air getting forced out backwards through the intake. When it hits the turbo, it "flutters" kind of like a horse's lips or something. However, it should only do that when you're into the boost and let off. FYI, a blow-off valve senses the difference in pressures on opposite sides of the throttle blades, and vents out that extra pressure. It does more on manual tranny vehicles (where they're on and off the gas more), but it will put less stress on your turbo if you do install one.
Depending on the type of "buzz", it could be something else. The U-joints on my S-10 are going, and when I let off the throttle it has a tap-tap-tap (well, more like clunk-clunk-clunk now) "buzz". The play in the joints lets it wobble some when the load is taken off the drivetrain...
