Brief high-pitched sound carried by Uncle Sam's transmitters (7)
I believe the answer is:
uplinks
'sound carried by uncle sam's transmitters' is the definition.
I know nothing about this answer so I can't judge whether this works.
'brief high-pitched' is the wordplay.
'brief' means to remove the last letter.
'high' becomes 'up' (associated in meaning).
'pitched' becomes 'plinks' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'up' with its final letter taken off is 'u'.
'u'+'plinks'='UPLINKS'
Can you help me to learn more?
(Other definitions for uplinks that I've seen before include "connections to satellite" , "Comms connections to satellites" .)