Thank you!!
Actually I managed to figure this problem out, but I appreciate the help. 🙂 Yes it was a dithering issue. Well done!
I did try mixing down to 32-bit instead, and it did fix it! Hooray! All better! No funny noises to be found. ^.^
Using Audition’s dither seemed OK after that. But I will check out this Mbit+ thingy and see if I can notice a difference in conversion quality.
Thanks a bunch. 🙂