How do you describe a "foam siren"?what does it mean?

Question

"I go to the kitchen side of the bar, where Leona's still working up to her brags; she has to empty Mom out first, so her voice slithers up and down, "Oh how neat, wow, Doris, oh great," like a foam siren."
(This is part of the novel"Vernon God Little"by DBC Pierre)

Do you think, it means the sound of foam, which is the same as the sound of a siren?

Answer 1

google only returns 4 hits for ''foam siren''

Answer 2

http://images.google.com/images?hl=en&q=foam%20siren&ie=UTF-8&oe=UTF-8&sa=N&tab=wi