Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
af-frĕmo (better adf-), ĕre, 3, v. n., to roar, rage, growl, or murmur at (only in post-Aug. poets): adfremit his (Mars), Val. Fl. 1, 528: Boreas stridentibus adfremit alis, Sil. 14, 124.