Shriek having lost a companion – it sounds like it sucks (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

“squeal”(shriek/a long high-pitched cry) minus ( having lost ) “ a ” + CH(abbrev. for Companion of Honour, one awarded for outstanding achievements in the Commonwealth). Defn: A soft sucking sound when pressure is applied to mud, the term being imitative of the sound it describes.