Most buzzes are caused by one of two things: "DIRTY" power or a lifted\non-existent ground. Allow me to explain;
"DIRTY" power is just that. It comes in and carries a lot of static with it. Most newer systems have filters built in on the power side of the main board. The fix? Try running your Magic Sing from a wall socket that doesn't have anything else pulling from that particular circuit. You should also invest in a GOOD power strip and not one that cost $5-$10 bucks. All these are good for is getting power to multiple products simultaneously, AND they don't have the resistors and filters to give you a constant 120v AC.
Monster Cable Co. was a very sought after item up to the point to where Radio Shack no longer carried their products.
If you really want to get your money's worth out of the instruments you buy, don't slack on the power strip. This will be the most costly mistake ANYONE can make.
Here is an article that explains what I did and gives you answers on how to fix this issue.
Hope this helps. Dirty Power What It Is and Why You Need to Clean It Up Schneider Electric...