There is a Ray Stevens song titled "Shriner's Convention" which, at around 1:05 in the linked version, contains the following one-sided phone conversation between two characters:
"Coy, why aren't you at the parade? What? Well, how'd you get that big Harley up there in your room?"
"What? I can't hear ya' Coy! Quit revvin' it up, boy! Turn it off! I just want you to know one thing: You have embarrassed us all, the whole Hahira delegation!"
"Now I'll see you at the banquet, son. And you be there Coy, you hear me? Black tie, seven o'clock! Be there Coy! And Coy, don't answer the phone, 'udden udden!'"
What is the meaning of "udden udden" in this context? At first glance it appears to be an onomatopoeic sound that a car or motorcycle engine might make, which makes sense since Coy has a motorcycle in his hotel room. The part that doesn't make sense is how Coy could have answered the phone in a motorcycle-like manner, and what prompted such an admonishment from the speaker in the first place.
This motorcycle theory is supported by some cursory research; the book "The Great Possum-Squashing and Beer Storm of 1962: Reflections on the Remains of My Country" by Fred Reed contains an instance of "udden udden" referring to the sounds of a car's engine. Aside from that, my searches haven't turned up much of anything.
I'm not even positive of the spelling. Some transcriptions of the lyrics have it as "uddn'uddn," and others omit the quotes around these words. If it is indeed a southern/rural contraction or slang term, it's not one I've ever heard.