Ghost-sound in my soundcard

Can anyone assist me with the following. About 2-weeks ago I watched a really interesting video on youtube.com (2012-Signs in the Sun, Moon, and Stars-Just The First 3 Months). Since then, the opening sound/music of the video (first few seconds) has been stuck in my my system - so I went back online and downloaded the video on to an external drive (to keep a record), and watched again. Nothing out of the ordinary happened, so I disconnected the drive (as I always do). However, the opening sound of the video is still stuck in my system, like a ghost-sound in my soundcard. Even when I am watching other videos/films on my system, this sound comes up... and even as I write this note in this forum i heard the sound from that particular video come up. How can I get rid of this recurring sound? Can anyone assist me with this? Much appreciated.
Cheers,
BudoNik

Is it possible that you or something may have accidentally assigned that sound to an event on your Mac? Open System Preferences, Sound. Click on the "Sound Effects" tab and see if you can spot the "ghost sound". If it appears there, just remove it.

... thanks for writing. That's the first thing I looked at, and there is nothing out of the ordinary in my sound system - everything is as it should be - "built-in." Under the tab Sound Effects, everything listed is "built-in." Under the tab Output I have the headphones (where I have my external Logitech Speakers plugged in, and have had those since I bought the system in 2009, and Boom-Device, which is a software program called Boom to enhance the laptop speakers when not plugged in to external speakers (an excellent program I highly recommend). I even went into my system/User's/Music and couldn't find anything resembling that "ghost-sound" file. I will keep looking in my system folder because I think you are correct, if not in SysPref's, then it has to be in there somewhere... for now, it remains a "ghost-sound in my sound system (btw I just heard it again, as I was writing this response).
Cheers.

Here's a link to an image of the ghost-sound file. Maybe you can look into it and guide me to delete:

http://img833.imageshack.us/img833/2448/screenshot20120415at125.png

BTW, I found a log file that shows the sound file from the youtube video played at 12:41 my time (GMT+2), which correlates with my earlier response, and again at 12:57. I took a jpg image of that fie to show anyone who can assist in locating it. I also include a copy of both logs below:

4/15/12 12:41:56 PM [0x0-0x24024].org.mozilla.firefox[370] *** nsHTMLElement::FinishDecoderSetup() mDecoder=0x1649f7c00 stream=0x160ba8000 src=http://o-o.preferred.forthnet-ath1.v9.lscache1.c.youtube.com/videoplayback?upn=rZ2N_KY8lYA&sparams=cp%2Cid%2Cip%2Cipbits%2Citag%2Cratebypass%2Csource%2Cupn%2Cexpire&itag=43&ip=130.0.0.0&signature=6CB67E9E0B2B2ED44F70B9C22D3A26EDA168CEA5.C49563429FE8B94CCD55CA99DC864CB0A2C2B2E0&sver=3&ratebypass=yes&source=youtube&expire=1334503878&key=yt1&ipbits=8&cp=U0hSSVVLUV9MUkNOMl9NRVVJOlFyQ1FKdnRPOF9h&id=320196ad7de3c49a
4/15/12 12:57:32 PM [0x0-0x24024].org.mozilla.firefox[370] *** nsHTMLElement::FinishDecoderSetup() mDecoder=0x164fce000 stream=0x15d771000 src=http://o-o.preferred.forthnet-ath1.v9.lscache1.c.youtube.com/videoplayback?upn=S7LCuIh0B5s&sparams=cp%2Cid%2Cip%2Cipbits%2Citag%2Cratebypass%2Csource%2Cupn%2Cexpire&itag=43&ip=130.0.0.0&signature=3171339A9573A93205A06181FE5DFA514E579A0B.BBFCC97A8DC043B00D64ADE6A45C687F99F0AED3&sver=3&ratebypass=yes&source=youtube&expire=1334503878&key=yt1&ipbits=8&cp=U0hSSVVLUV9MUkNOMl9NRVVJOlFyQ1FKdnRPOF9h&id=320196ad7de3c49a

Let me know further.
Cheers.