Green’s Dictionary of Slang

chank v.

[? SE champ or echoic]

(US) to eat noisily, to chew loudly.

[US]Monroe & Northup ‘College Words and Phrases’ in DN II:iii 137: chank, v. To chew loudly.
[US]Courier (Lincoln, NE) 12 Apr. 8/2: It is racking to catch a pupil every now and then chanking candy.