Avid Juicy Sevens Howl Like a Banshee When Wet! WTF!!!

This has been an ongoing problem since I got the bike just recently. I bought it used, a 2003 Santa Cruz Blur XC. In the dry, these work great. Riding in snow, the snow granules melt when they hit the hot rotor and these brakes howl and squeel and just plain ole don't work well when wet.

I have tried the following:

* Cleaned the 160mm rotors w/ brake cleaner. Even used a little scotch brite to help remove any glaze/contaminants from the rotor surface. And then I cleaned them some more.

* Ran the pads in a figure 8 pattern on some sandpaper, washed them in brake cleaner. Then In hot water to make sure no contaminants. Let them dry overnite. Pads are Avid B4-R/B4-L pad pairs each caliper.

* All mounting screws are tight. I mounted up & tightened the calipers per Avid manual instructions. I have the 4 concave/convex washer pairs on each caliper as specified.

I Checked the bike over for loose frame & pivot bolts, loose spokes, loose wheel bearings, anything that might contribute to chatter. All seems well. King headset is snug. No obvious abnormal wear in the fork.

The only thing I found is that I think one of the pistons on the rear brake caliper may be stuck. As it deflects the rear rotor when the caliper actuates. And it doesn't appear to move. But that doesn't explain why the fronts howl too.

I'm going to address the sticking piston issue. But I guess I should try new pads. What pads work well w/ Juicy-7's and aren't prone to howling? I'll do some more searching on the forum and see what I can find in the meantime.

Thanks in advance.