I can't reproduce the problem here. What program are you using to convert the file? Have you tried another program (such as Audacity)? Please upload the actual ogg file you are having the problem with so I can see if there is something unique about that particular file's data that could be causing the weird behavior.
Which library plug-in has the problem(or do they both?)
You can get this from the Console output. I assume you are using SoundSystemJPCT, but that doesn't tell me which library plug-in you are experiencing the problem for, because SoundSystemJPCT will either load the LWJGLOpenAL or JavaSound plug-in, depending on your OS and what components / drivers are installed. Also, you might try using the CodecJOrbis plug-in to see if it also has the screeching behavior, since JOrbis has been around for a while and is well supported and more compatible than the JOgg codec plug-in which ships with SoundSystemJPCT.
--EDIT--
I decided to read back through this thread to figure out when it was that I experienced this screeching behavior before (3 years and 26 pages worth of history here). I finally found it, but unfortunately, that earlier problem does not apply to your case, because it was related specifically to playing MIDI through a javascript interface I was working on at the time:
...
4) I was having problems with loud scratching sounds in some browsers the first time a sound is played. To compensate, I had to make the javascript automatically play a silent MIDI file when it starts up. This is completely transparent, but you are required to place the file "silence.mid" wherever the javascript is located.
...