Men surrounded by clamour turning up and eating away (7)
I believe the answer is:
erosion
'eating away' is the definition.
(synonyms)
'men surrounded by clamour turning up' is the wordplay.
'men' becomes 'OR' (Other Ranks: non-commissioned soldiers).
'surrounded by' means one lot of letters goes inside another.
'clamour' becomes 'noise' (I've seen this before).
'turning up' says the letters should be written backwards.
'or' inserted inside 'noise' is 'noisore'.
'noisore' reversed gives 'EROSION'.
'and' is the link.
(Other definitions for erosion that I've seen before include "A wearing away as of rock by water" , "The gradual wearing away by weather" , "Abrasion" , "Wearing away (of soil, rocks etc)" , "Action of wearing away" .)