Audio Systems: Unique Volume cutout and reception combo, correct quality, reception problems

Question
I bought a  BOSS 3130R-MP3 car radio off of Ebay a couple of months ago.  The problem was immediate. Let me just go down the facts:
If I start up my car after it has sat for awhile the radio works fine.  I can scan for a million channels (Charlotte, NC).  The reception is great.  If I drive around for awhile (varies 5-20 minutes usually) the radio will start to sound as if it's having reception problems.  It's a unique sound.  It's not static.  It's a cutout of volume.  It starts small, pulsates between half volume and whatever volume control level I had it on.  It wavers almost...then after a minute it permenatly cuts to half volume and stays there. When this is happening it happens accross the entire band, it does not matter what station I select.  It's consistent all over.  Every once in awhile (after I have it on 100 volume level to hear it) it will try to go back to normal volume (only it's trying to get to the VERY loud 100 setting from it's muffled state).  When this happens I can no longer scan and find ANY station.  It continously cylces through the entire FM band and finds nothing.  I can manually find stations, however.  When it is "cutout" the quality of sound is not hampered, only the volume is halfed and I can no longer scan for stations.  I have tried several things that only add to the mystery.  With the car on and radio in my hands (half installed) I waited until it did its "cutout".  When it did, I unplugged the antennae connection (which is through an adapter to fit).  This caused NO change at all.  Upon plugging it back in, there too, was no change at all.  While it is in "cutout" I can switch it to the MP3 player and everything is fine, volume is correct, quality is perfect.  This is always so.  Now, if it is in cutout and I turn the car off, I have to wait a long while for it to "reset" back to normal.  Sometimes this is hours.  I have researched a LOT on this, and nothing quite matches my problem.  Some say antennae, but if that is so then why can I get perfect reception in the first place?  Others say it's electrical noise from my fuel pump!  I'm begining to think its interference from the mother alein ship!!  I'm stumped.  I am hoping it's a defective radio, but I've never had such a thing happen.  

PS: I am sure it's installed correctly, I used the correct wire harness and triple checked the connections.  Nothing is loose that I can tell, but I'm willing to try anything.  I drive a 1994 Saturn SL1 with 150K miles on it.

Answer
Chad,
The problem sounds like something in the FM receiver front end is failing, Or something in the stereo decoder circuits is failing. Try this test, With a good station tuned in and with the stereo indicator lit up when you tune to a good station, watch what happens when the stereo starts acting up. If the stereo is having a receiver problem the stereo indicator will go off/out when and if the receiver is failing. If the stereo indicator remains lit when the stereo starts acting up the problem is with the audio preamp section between the stereo decoder and the audio output section.

TOM,
T&D ELECTRONICS
tdeser@zoominternet.net