Glasses? They can make high-pitched sounds (6)
I believe the answer is:
flutes
I believe this is a double definition.
'glasses?' is the first definition.
(flute is a kind of glass)
'they can make high-pitched sounds' is the second definition.
(Other definitions for flutes that I've seen before include "Musical instruments as for James Galway" , "Pipe-like musical instruments" , "High-pitched woodwind instruments" , "Wind instruments as played by James Galway" .)