Car Stereos: Speaker Pop, sony speakers, stock speakers

Question
Hi Scott, My son and I installed an after market stereo (Boss BV9055 80 watts x4) into his 2003 Mercury Mountaineer. We wired the stock speakers to run off the new head unit and also wired up 2 pair of Sony XS-GT6935A speakers (peak power 300 watts, rated power 60 watts). The new Sony speakers are powered by wires we taped into at the head unit which go to the stock speakers in the doors. When everything is connected and playing loudly all the speakers sound "fine". Of course the stock speakers in the doors are distorted but they sound ok and the 2 new pair of Sony speakers sound great. (Head unit volume runs from 0 to 39. At 35 they still sound great). Here is my problem, however. When we turn on the car and ramp up the sound (volume 26), the new Sony speakers pop or crackle; but only when the car is on. The speakers in the doors still sound the same, distorted but no pop or crackle. The pop or crackle coming from the new Sony speakers does not change when the engine rpm changes so it does not seem to be related to alternator interference. We can not understand why we are getting speaker pop or crackle from the new Sony speakers only when the car is running. Another symptom is that the pop or crackle becomes much more pronounced when the bass is increased. If you have any thoughts as to our problem that would be great. Thanks Scott!
Bruce

Answer
Bruce,

That does sound strange.  Apparently the extra couple of volts while running is causing some type of overpowering.  Are you sure the wire at the stereo goes directly back to the doors where the new speakers are installed?  Sometimes certain cars have built-in amplifiers that are preset for stock radios.  If the aftermarket stereo has more power than the stock stereo, it could be overpowering the inputs of the amplifier, causing it to cut out.  The only other thing that I can think of is that the wiring going to the New speakers is not adequate.  And new wires should be run to new speakers.  Hope this helps, Scott