Check the air pump. It is rignt next to the crankshaft, on an 87 V6 it is below the alternator on the passenger side. I removed my air pump, put a shorter fan belt on to accomodate the short belt requirement. Cleaned up the sound quite well!
Here's how you can check it -- remove the fan belt from the system and start the engine. Is the engine quiet? If it is, then the noise is definitely from an accessory not from the crank. Be sure to not drive the car since you will NOT have a water pump!
Take the belt off and clean it with a stiff bathroom brush & soapy water (you already soaped it up!) Soap, et al, is not going to help the noise on a serpentine.
--Mark
http://www.marksatterfield.com