does anyone know of any episode where shaggy says the line 'i don't like the sound of that'??

I don't think he's ever said it as a stand-alone quote, but he's said it in a sentence. In What's New Scooby-Doo, the episode "There's No Creature Like Snow Creature", he says "I don't like the sound of that 'hmmm'." This instance is also spoken by Casey Kasem, the original Shaggy's voice, if that matters to you.

Also in "Coast to Ghost", one of the episodes in the 13 Ghosts collection, someone says "Hmm, I don't like the sound of that music, or of that name, Professor Fantazmo." I'm not sure it's Shaggy, though.

Hope this helps! = )