There is an American English dialect/accent that pronounces words like "heard" and "bird" as "hu-yd" and "bu-yd". One example of this would be CCR’s song "I Heard it Through the Grapevine". Another is LaMonica Garrett’s character in the series "1883". It’s fairly subtle, but still distinctive and although I’ve often heard it, I can’t place it geographically.
Can anyone help identify it?
Short answer: Brooklyn English and New Orleans English.
Longer answer: at present, virtually no still-spoken varieties of American English feature this merger, but in the past, it was common in some accents in New York (stereotypically in Brooklynese) and in New Orleans English.
What we hear in Creedence Clearwater Revival’s version of I Heard It Through the Grapevine is called the curl-coil merger.
Here’s some of what the Wikipedia article has to say about this merger:
In some cases, particularly in New York City, the NURSE sound gliding from a schwa upwards even led to a phonemic merger of the vowel classes associated with the General American phonemes /ɔɪ/ as in CHOICE with the /ɜr/ of NURSE; thus, words like coil and curl, as well as voice and verse, were homophones…The merger is responsible for the "Brooklynese" stereotypes of bird sounding like boid and thirty-third sounding like toity-toid.
This feature of the Brooklyn accent is, let’s say, old-fashioned. According to the same article, virtually no native New Yorkers born after 1950 speak this way. This feature of Brooklynese remains familiar to younger people because of cultural artifacts from the early 20th century, such as The Three Stooges or Bugs Bunny.*
But John Fogerty, the lead singer of CCR, is not singing with a Brooklyn accent. It’s more of a New Orleans accent, as would befit the singer of Born on the Bayou.
That same Wikipedia article explains that, although most American Southern accents are "non-rhotic" (they don’t pronounce /r/ after a vowel, unless there’s another vowel sound after it), they do not feature the coil-curl merger. An exception was the New Orleans accent.
However, as in Brooklyn, this merger is dying out. Old blues and (Black) rock and roll singers that Fogerty admired may have spoken this way, but very few people in New Orleans (or anywhere) speak like this today.
*According to Bugs Bunny’s voice actor, Mel Blanc, Bugs actually has a Flatbush accent, which is equal parts Brooklyn and Bronx (https://walkoffame.com/bugs-bunny/).