Green’s Dictionary of Slang

to talk, to chatter, to gabble; thus yattering n., (idle) chatter.

1821–5		‘Bill Truck’ Man o’ War’s Man (1843) 38: Aye yattering and yelping whan ye’re eating.
1825		Jamieson Etym. Dict. Scot. Lang. (Supplement) II 703/2: She’s ay yatter-yatterin, and never devaulds.
1831		Gasometer 457: She yattered about an ugly man that cam’ in a fiddle case.
1844		New Sprees of London : Why, my tulip, if you think my palary is queerums, if you've not got faith, it's no use to yatter to a Jos.
1936		E. Pound letter 25 Apr. in Paige (1971) 280: That wdn’t be as dull [...] as merely trying to yatter about wot he wrote.
1946		(con. 1912) B. Marshall George Brown’s Schooldays 47: Stop that yattering there.
1947		N. Streatfeild Grass in Piccadilly 244: She would bring Freddie and Dougie, must have someone to yatter to.
1970		La Motta, Carter & Savage Raging Bull 24: We could hear all these guys yattering.
1997		P. Theroux Kowloon Tong 153: Here, Hong Kong was not a frenzy of marketeers and plonkers yattering on cellular phones.
2005		H. Mantel Beyond Black 167: The women were approaching, his missus rolling towards him, her pal skipping and yattering and twirling her car keys.