Tube from what we hear must be avoided (6)
I believe the answer is:
ducked
'avoided' is the definition.
(ducking is a kind of avoiding)
'tube from what we hear' is the wordplay.
'tube' becomes 'duct' (I've seen this before).
'from what we hear' indicates a 'sounds like' (homophone) clue.
'duct' is a homophone of 'DUCKED'.
'must be' is the link.
(Other definitions for ducked that I've seen before include "was plunger?" , "Dipped" , "Avoided as mallard might" , "Went down" , "Bowed head to avoid missile" .)