98 Windstar - Grinding noise at stoplights

Lately my van has been making a bit of a grinding noise (although not like metal rubbing - more like a fast, low frequency noise) when stopped at stoplights with the transmission in drive. Once I get going again the noise stops. Noise doesn't seem to be present normally in park (faint sometimes), although the engine RPM are about 200 RPM faster in park so if it's a weird noise on something like an idler pulley I guess that might make a difference...

Transmission fluid looks nice and clear pink/red. Seems like it might be a little full, but I've only checked it when the engine is off, so I'm not sure if that would make the level go down significantly.

Anybody have any ideas?

I'll bet it's your ABS kicking on when it doesn't have to. Best way to describe the sound ABS makes is . . . . . as if you were to braking while on the grated part of a drawbridge. Does it sound like that? If so, check ABS.