Why would my left side speakers front and rear be quieter than my right side speakers for car audio and this is a brand new system all the settings are normal including balance and fade?

there should be a "balance" and "fader" feature on your stereo. check the manual as to how to adjust these. the "balance" feature adjusts left to right. make sure that it is set to 0, then the left and right will be even.

You might also have some loose connections.