From The Works of Peter Pindar, Esq., Vol 5 by Peter Pindar (London: J. Walker, 1801), page 412:

WYATT
TO POINS, IN PRAISE OF LIBERTY.

To crawle in courtes is bondage harde!
For who y chooseth chaines I wot?
Yet some, for pleasures of rewarde,
Wi flatter—and blow colde and hot.

But Liberty will I emplore,
Though Poverty knock at my doore.

What be our wants?—some thinges, not all.
Contentment lyeth not in heaps;
Who hath a littel field, though small,
It grete is, if enough he reaps.

Then Liberty will I emplore,
Though Poverty knock at my doore.

[I found many other instances of the expression "poverty is knocking at the door," etc.]

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From Hiram Greg by J. Crowther Hirst (London: Richard Bentley and Son, 1881), page 77:

Among them were large numbers of handloom weavers, who, with a sad, sardonic humour, described the noise made by their looms as "poverty knock, poverty knock"....

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From Notes and Queries, Series 7, Vol. 4 (London: John C. Francis, 1887), page 328:

"Poverty Knocker."—In Oldham a weaver is sometimes called a "poverty knocker." I am informed that the sound made by the picking-sticks, which send the shuttle from one side of the loom to the other, is construed by weavers into "poverty knock"; hence the phrase. Can any of your Lancashire readers inform me whether the above is correct? J. Butterworth.

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From ibid, page 396:

"POVERTY KNOCKER" (7th S. iv. 328).—This phrase is well known in the West Riding of Yorkshire, but is not in such general use now as it was forty years since, when hand-loom weaving was still common in the outlying districts around Leeds. The phrase can scarcely be an onomatopoeia, as the simple click of the picking-stick of the hand-loom can only by a most vivid stretch of the imagination form the words "poverty-knock." Here the words were used contemptuously of a hand-loom weaver, whose earnings were much less than those of a power-loom weaver. Most probably the words have a reference to the timid single knock, such as is made by a poor beggar, as distinguished from the more fashionable rat-ta-tat made by a person who "knows manners." I well remember many years since hearing an old hand-loom weaver (who dwelt on a wild moorland road leading into the Slaithwaite valley) say that he could almost tell a poor person from a well-to-do one by the kind of knock he gave at his cottage door when asking the way across the moor on a dark night.

Alf. Gardiner.
(Mr. Herbert Hardy writes to similar effect.)

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From The Ragged Edge: A Tale of Ward Life & Politics by John Thomas McIntyre (New York: McClure, Phillips & Co., 1902), page 125:

"It's Nelly Fogarty," said someone. "She don't look like a poverty knocker when she's dressed up, eh?"