ok i might not be the mating sound but mine both only make this crazy little 'oink oink oink', when Mr Quail is on Mrs Quail and doing his thing. Its alot diffrent from their normal "hey, where'd you go?" sounds.
He also does this "come here, ive got this for you" noise which is a 'thunk thunk thunk' where he lowers his head when he gives a treat he's found.