So we had a spot of nasty weather last week (rainy slippery roads) and I shifted my 2000 2nd Gen 1500 into 4H. I drove it those two days, 20 miles total for both days and promptly forgot I had it in 4H and then drove it an additional 140 miles to the beach and back. The speed on that trip varied but got as high as 70 mph for lengths of time as long as 40 minutes.

Now I'm hearing a rattling sound on the front end when I'm in 4WD. In 2H there's no noise. Ideas, other than I may or may not be stupid?

Should be fine then.

Have a look at the front U-joints.

Did the 4WD light come on? Hard not to notice that.

I'd check the u-joints on your front axles and the front driveshaft. I'd lean towards the axles more as they don't like to turn under stress on the road. In dirt or snow, there is some slippage.

Funny you should mention that. The light hasn’t been working for a short while, even prior to this.

Does the lite test at startup? I would wonder if the front axle was actually engaging....

It was working a month or two ago, but the light hasn't worked for a few weeks and the start up sequence doesn't light it either. I probably wouldn't have used 4WD this past week if it hadn't been for Debby. I really don't use or need it that often.

You can test the circuit, and the bulb easily enough, just unplug the electrical connect from the switch on the CAD, and jumper the pins in the connector. Make sure it isn't grounding out on anything, then simply turn the ignition on. 4x4 light should come on. If it does, then you likely have a vacuum problem, and your 4x4 isn't actually working.....

I would pull the plug in the diff, I think it has a magnet? Also check the front driveshaft. It doesn't spin under power in 2wd from either direction. Specifically the CV joint.