This is about my 2001 Dodge Dakota pickup truck, 3.9 V6 with a manual 5 speed, 151,000 miles on it now. Truck still has its original OEM 117 amp Denso alternator. I replaced the belt tensioner/pulley assembly at about 43,000 miles, and I replaced the idler pulley at about 70,000 miles, both with Napa OE grade parts. My serpentine belt has maybe 15,000 miles on it and is good shape. I replaced my AC compressor, receiver-drier and fixed orifice tube at about 75,000 miles, due to noise in the AC compressor. I used a Napa compressor and Carquest receiver-drier. My AC is ice cold, has the correct freon charge and works great. Today my wife and I drove over to Orlando for a July 4th get together, drove about the first 15 miles in very heavy rain, it started raining just as we left home. A few blocks from home I noticed my voltage gauge needle was down just a bit, I did not think much of it because I had just turned on the AC and fan on high. Volt needle came right back to middle of the gauge as normal. I drove another 5 miles or so, still in the rain, but it was just not quite as heavy. At at red light I noticed a squealing noise from under the hood. It got a little louder as I went on through the light. I got out on the turnpike, the squealing noise was still there. Stopped under a bridge to check it out, the squeal was not there at idle. If I gave it throttle by hand, I heard the squeal pretty loud, it sounded like it was coming from the alternator. I put a long screw driver on the alternator and put the other end to my ear, it sounded to me like the noise was in the alternator. I drove on to Orlando, not too far, the squeal was there all the way to our friend's house. It quit raining about the time we got there. Truck sat for a few hours while we were there, we headed home and I have yet to hear that squealing noise again. I got home and pulled off the belt, the idler pulley spins freely and has no noise to it when I spin it by hand. The alternator pulley feels rough and a little hard to turn when I turn it by hand. All other pulleys turn OK. I listened to the alternator case and the alternator pulley shaft with my cheap mechanic's stethoscope, I can only describe the sound as a howling noise with a bit of a grind to it. Problem is, I don't know whether that is how the alternator pulley is supposed to sound and feel when spun by hand..Also, is the alternator pulley supposed to spin freely like the others or is it normal to have some heavy type feel to it? I have 12.65 volts at the battery with the engine off, 13.70 volts at the battery when the engine is on and 13.75 volts at the battery with the engine on, AC and high beams on and manually holding the throttle open at about 1500 RPM's. I believe the alternator itself is working OK but my question is is the pulley going bad? I tried spraying the pulley and its shaft with water to duplicate the rain I drove through today, it still did not make the noise here at home. Thanks for any help on this. I am kind of stumped.