This sounds like a difficult topic.
You could try looking at the following:
ERIC website – Education Resources Information Center.
Islay Cowie and Sun-Ah Jun (department of linguistics, Ohio State University) wrote an article on pronunciation differences in Korean – English bilinguals. This isn’t the same as Korean learners of English but I think you’ll need to broaden your references.
I saw a reference to an article by Hwang and Schafer of Hawaii University on the net but I haven’t seen the actual article.
Also try the following links:
http://www.humnet.ucla.edu/humnet/lingu ... ma-Jun.pdf
Humnet’s report compares Japanese English and Korean English intonation.
Covers voicing interference.
http://www.coli.uni-saarland.de/publika ... 97:SSD.pdf
This articles goes into the pronunciation problems of Korean learners of German. German and English are both stress-timed languages so you might get some inspiration from this source.