high pitch noise

So I have an (older) Kenwood DNX7120 DVD/GPS head unit in my 04 Silverado. I've been getting a super high pitch "squeal" out of the blue. When it happens, my head unit starts rolling through the different modes it has, tuner to dvd to video and then stops once it's found a mode in which it...

I have installed a new car audio system with one 4 channel amp and with a mono channel amp for the subwoofer. I bought everything brandnew (including high quality cables) . But I hear really annoying high frequency noise when i start the engine. How can i get rid of that noise? and what are the...