The Collaborative International Dictionary of English v.0.48:

Clatter \Clat"ter\, v. i. [imp. & p. p. Clattered; p. pr. &
   vb. n. Clattering.] [AS. cla?rung a rattle, akin to D.
   klateren to rattle. Cf. Clack.]
   1. To make a rattling sound by striking hard bodies together;
      to make a succession of abrupt, rattling sounds.
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            Clattering loud with iron clank.      --Longfellow.
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   2. To talk fast and noisily; to rattle with the tongue.
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            I see thou dost but clatter.          --Spenser.
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