It might not be a bad idea to get new washers and nuts and search this forum for the right torquing procedure. I seem to recall you had to torque to a certain tightness, loosen a little then torque to the final spec, but I'm not 100% sure. Another option is to use this opportunity to buy yourself a big torque wrench and the right sized socket to augment the tools you own (though I prefer to bring my vehicle in for some attractive service manager of the fairer sex torque my nuts)The clicking is back. It's only when I take my foot off the accelerator pedal (I drive in L only). So instead of going back to the dealer, I'm taking the Volt to my nearby trusted all-purpose garage and having them "torque my nuts". Is this a bad idea? What's the worst thing that could happen if I just ignore the sound, and pretend that I can't hear it? Will the bottom of the car fall off? Is this a real problem or an imaginary one? I really don't know how much time and money to devote to/waste on this subtle, harmless little clicking noise....
As for whether this is necessary, anything in the drivetrain and suspension that makes noises means that something is wearing out or loose. Over time parts may break or fall off. I'd much rather have something superficial fall off (muffler, bumper, antenna) than something integral to keeping your car on the road. So don't ignore this.