Gordon Johnson, managing director at Axiom Capital, said the issue is China.
"You're seeing a significant slowing of growth in China due to a reduction in credit," Johnson said. "That's affecting the commodities sectors and that's not reflected in stock prices or valuations."
Caterpillar hasn't been the only mining equipment supplier to feel the sting of slowing activity. Swedish rivals Atlas Copco and Sandvik highlighted falling demand from mining customers in their quarterly updates. Together both companies supply more than half the world market of underground mining equipment.
(Read more: China July flash HSBC PMI plunges to 11-month low)
"The low investment levels from miners continues to be noticeable for this part of our business," as the industry focuses on cost control and capital efficiency, Sandvik CEO Olaf Faxander said in a statement.
The slowdown has even hit the U.S. rails. Norfolk Southern CEO Wick Moorman told CNBC, "Our export coal franchise, which is aimed at the metallurgical markets, has probably suffered a little more than some of the other franchises."
He attributed it to slack demand from China, Australia's improved competitive position as the Australian dollar weakens and a struggling European economy.
"Global conditions are really what influence the price of metallurgical coal worldwide," the Norfolk Southern CEO said. "It's something that will take a while to work through, and it's something that we'll work through, as well."