Sneaking feeling/suspicion

As a verb, to sneak means to move or creep along in a furtive, secretive manner and derives from the Old Norse snikja to creep or crawl. Sneak has been used in this sense since the late 1500s. Sneak as in a mean-spirited, despicable person dates from the early 1600s. Its adjectival use, as in a sneak attack, is American from the mid-19th century. Use of the present participle, sneaking, to describe a vague, uneasy feeling or suspicion is much more modern and dates, according to the OED, from the early 19th century.