Beam in part of garden made a beastly noise (6)
I believe the answer is:
brayed
'made a beastly noise' is the definition.
(I've seen this before)
'beam in part of garden' is the wordplay.
'beam' becomes 'ray' (synonyms).
'in' indicates putting letters inside.
'part of garden' becomes 'bed' (flower bed).
'ray' inserted within 'bed' is 'BRAYED'.
(Other definitions for brayed that I've seen before include "Made sound like donkey" , "Made noise like donkey" , "Laughed like a donkey" , "made an ass-like sound" , "made nasty noise" .)