Rule 1: don't buy any of your shit from wal-mart.
Rule 2: Make sure your Negative ground wire from the AMP to the car is touching raw metal, and not Painted Metal. Use like a Steel-Wire Tooth brush to rub some of the paint off.. depending on where you go to connect your negative wire to the car.
I always Recommend after market radio, Make sure its got a good Aux/usb port, and make sure the bluetooth supports android/iphone sounds for music, and not just phone calls ha ha.
Used to be the biggest complaint.... people returning radios to wal-mart and be like the bluetooth music isn't working, or when bluetooth music is on, it don't work with subs ect.
USB/aux always provides the best Quality over wireless .
if you are someone who has unlimited cellphone/mobile hotspot ect.
I recommend a touch screen radio, because phone to radio via aux/usb cable can also lose Quality sometimes.
Just these small little things will make the difference.