The OED gives credit for "gruntled: Pleased, satisfied, contented" to PG Wodehouse as a backformation from gruntled.

Older 16th cent. words, however, include:
verb Gruntle: 1. To utter a little or low grunt. Said of swine, occas. of other animals; rarely of persons. 2. To grumble, murmur, complain.

Noun Gruntle: 1. The snout of a pig, or other animal. 1.b. transf. The face of a man, etc. 2. A little grunt; a subdued grunting sound.