They make a high-pitched noise when they're pretty heated

TEAKETTLES

Think of whistling kitchen items that boil water; they often have a spout and are used for making tea.

This clue plays on two meanings of "heated." First, it hints at something literally getting hot—like a teakettle on a stove. The second part is a pun: when water in a teakettle boils, it whistles with a high-pitched noise, tying back to "pretty heated" in a clever way. The answer is the plural form because crossword clues often expect common objects in their standard usage.