I had an amp installed and all the speakers replaced in my truck. There's a faint distortion in the right front door speaker, since installation. The faint distortion is more noticeable during conversational programs. It does not matter if I'm listening to AM, FM, XM, or even a CD. It also does not occur all the time. But does not seem to be temperature, time of day, or weather related, but more related to frequency. I can minimize the distortion by turning both treble and bass down. My wife cannot hear it, but I can. The installer has replaced the speaker, replaced the crossover, replaced the amp, rewired the speaker, and set the gain on the amp several times. I'm wondering if the factory head unit is the issue, given the unit is tuned toward the cheap factory speakers. However, the installer switched leads at the amp from left to right, and the problem remained at the right front door speaker. There are units on the market to "clean" the factory head unit signal, but at their given costs, a new head unit may make better sense. Specs are below. The installer has an excellent reputation, and has bent over backwards to resolve the issue. I'm not concerned about him, since he shares my concern over this issue. It is rather perplexing. Any ideas or things to check would be most appreciated.
Vehicle: 2007 GMC Sierra Extended Cab (New Body Style)
Factory System: Non-Bose AM/FM/CD/XM Head Unit, 6-1/2" factory speakers in front doors, 4x6 factory speakers in rear doors, 1" factory tweeters in A-Pillars.
Modifications Made: Added Memphis MClass MCA2004 Amplifier, Memphis MClass CoAxial 6-1/2" Speakers 15-MC6 in all four doors, Memphis MClass15-PR1 1" Tweeters in A-Pillars. Factory head unit with XM remains.
Memphis MCA2004 Amp Specs - RMS Power 4 Ohm Stereo (14.4V) 50x4 / Input Sensitivity 250mV-9V / Frequency Response +/- 1dB 10Hz-50kHz (Amp feeds are via LOCs located behind the factory head unit.)
Memphis 15-MC6 Speaker Specs - RMS/Peak (W) 50/100 / Sensitivity (dB) 93 / Carbon Fiber Cone / Magnet Size (0z) 10 / Mounting Depth (in) 2.25
Memphis 15-PR1 Tweeter Specs - RMS/Peak (W) 50/100 / Sensitivity (dB) 87 / Mylar Cone / Magnet Size (0z) 0.75 / Mounting Depth (in) 0.75