AtD translation: Ggbbmmhhgghhkkhh!

[Mike Jing]

P605.21-606.5   Assuming he was not here only to deliver another gentle
suggestion from Scotland Yard to back off of the Gentleman Bomber case, Lew
took from an inner pocket a Tarot deck thinned to the twenty-two Major
Arcana and dealt them one by one onto the table, between the remains of a
vegetarian haggis and a platterful of pea fritters, until Aychrome began to
nod frantically and wave about a finger dripping with what Lew hoped was
only treacle. “Ggbbmmhhgghhkkhh!”
       Indeed. The card was not Renfrew/Werfner’s number XV after all, but
XII, The Hanged Man, whose deeply veiled secret meanings always seemed to
place it in a particularly critical area of investigation.

What's the inspector trying to say with the “Ggbbmmhhgghhkkhh!”?