Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
con-frĕmo, ŭi, 3, v. n., to sound aloud, resound, to murmur loudly, etc. (poet. and rare): confremuere omnes, Ov. M. 1, 199; Stat. S. 1, 6, 72: confremit et caelum et … circus, Sil. 16, 398: collis, Stat. S. 1, 4, 14.