Deep metal "groaning sound" from hitch. Is this normal?

I've had my Equal-I-zer for 16 years. It makes that noise. Nature of the beast. I think most of the noise is from the hitch head where the bars are inserted. Back when I bought mine, they didn't offer the nylon jacket for the L brackets but did recommend a bit of grease on them, as well as the flat, horizontal surfaces of the hitch head. The sway control is still there with the grease on those parts. I've learned you have to grease that hitch head every trip.