clipping? why?

Hello all. I have a 4 channel alpine amp, rated at 75W per channel (@ 4 Ohms) connected to my 4 ohm 2-100W RMS alpine coaxial speakers. I am using a BOSE head unit in a Mazda3 as my receiver. I calibrated my speakers using a multimeter and the voltage formula and discovered my max voltage to be 20V. Thus, I enforced this max voltage at volume 25 (which is ~2/3 of the max 33 volume). I then backed off a tad on the gain from this number. In total, the gain on the amp is only a tad over 1/4 of the way. I am getting random clipping in different speakers at different times. I drove 2 hours last night, and listened to loud rap music, and NO CLIPPING at all!!! I put on some soft rock tonight after just starting the car and with my volume level at 14, and the right speaker begins to furiously clip and only stops when I turn the main volume to 10 or under (which is very soft)...This also happened once a while back, but in a DIFFERENT speaker and ceased for a while. Well, this time, it happened on my 5 minute drive to a friend place AND on the way back after having the car off for a few hours. Why would this be happening?? Does this seem logical at all or any idea why the signal would be clipping?!?!

Clipping or distorting? 

At the amp, switch the Left and Right RCA connectors.  Does the problem move to another speaker?

Are you using the head unit out signal into the alpine amp, or the blose amp out signal in to the alpine amp? I have had 0 luck with blose amps for an input to another amp. Amping an already amplified signal just seems to not work very well. Too much chance for noise to enter the signal stream.

Obviously check the grounds etc...

To master and control electricity is perfection. *evil laugh*

You don't mention what year mazda 3, but pac-audio.com has an interface AOEM-MAZ2, for an 06 model, that is a t harness and gives you 4 channel rca outputs and a turn on wire...

A Bose system?  Did you disable the Bose amps?Support the12volt.com