Hi first this issue just started happening after i got my engine rebuilt so im not sure if it has any relevance.
Im not a avid audio junkie so bare with me as i only have a basic understanding of how a setup goes. i had a panasonic deck b4 and i noticed everytime i went over a bump or stoppped suddenly my back speakers would turn off/sound very muted. then i started noticing my right passenger speaker started cutting out aswell. So i took it to a local car audio shop and they took a look at it and suggested for me to get an new deck as it is the cause. So i didnt want to spend alote so i tossed in a sony cdx-gt300(red display matches my dash). so in the parking lot everything was fine all four speakers working. Then i pulled outta the parking lot got to the first light stopped and the passenger and both rear speakers stopped working again. So brought it back and they said it was a faulty deck again replaced it with the same model. Once again everything worked fine. started driving hit a slight bump and it happned all over again. I was fed up with that local store so i went to another and they told me it is my deck...ummm k???
So now i scratching my head trying to figure out wtf changed between then b4 my engine went and now besides my deck...?
 
is it the just the speakers or does the deck go out too.  .
 
The wiring.
I bet somethin isn't connected good or somethin is shorting out.
-Seth
 
 
ya im gonna say its going to be a bad ground connection its what is most likely causing it it is probably loose so when you hit a bump or something it loses connection for the most part...
 
ok its either the ground  or the wires running to the speaker  either some where along  the lines runnin to them they might have  pieces  nicked outa them or w/e  if its not that then the last thing i would say check would be the connections thats attach right to the speakers is may be lose and  when u brake  they might cut out since momentom is movin
but  in all honestly i think its the ground to   i would probly say when u went back for the new deck install they just switched the harness qwiuck over  and got u on ur way  when  they should have redid all the wires again with new tape or w/e that shoped uses to cover the wires 
so ya  if i was u man just take the  peice around the deck off witch is only 2 screws   witch u will see when u open the glove box  
take that off and u will have just the deck sittin  in the dash 
there should only be 2 screws holdin the deck in place to one on the top right side of the deck and bottom left side
now take them out and the deck will slide right out  take it out  and check the wires  make sure to take the tape off all of them  one at a time and retape them  but the ground is the solid black wire  make sure u check that  for sure  
do not  put the deck back in  u can test it with out puttin it back in just  put like one of the screws back in  to hold it and take it for a lil whip around 
if after all that it still does it then maybee where the ground is grounded to the  car is bad so  take  where the black wire  ataches to the deck  and just run a new one  to some where on the  car ok  
well thats about all i can say man hope it helps  if u need more or w/e and u live in toronto or some where around  there   get ahold of me pm me or something and i'll take a look  later
 
well this 13 ill be having a complete removal and install of the entire system again, its been rather anoying because ive been told everything short of miniture ufos dancing on my speakers causing them to short out lol.i could take out my deck but i was told if i touch it it would void some magical warrenty so i havnt as of yet. and just recently my car is having very bad ignition problems so ill probly miss the apointment and wait another two damn weeks lol
 
man i couldnt have givin u a better walk throught there  thats would be the reason why no one else posted after me probly but seriously man try it urslef no one will be able to tell honestly man  its simple u really gotta stop waitin for  @!#$s to do the work for u and just try it for urself or how will u ever be able to fix anything urself 
most of these guys on this site do there own work and hell its just a deck  not that hard u know  i vote that u just try to do it urslef  but w/e up to u
 
dont spend time fixing what the shop screwed up. they said the problem was your headunit so u forked over cash for a headunit. go back to them and demand that they fix the problem.if they say well its not the headunit its something else. then demand that they take their headunit back  and put your old one back in. they did not fix the problem youwent in for. they are just charging you to throw new equipment at the problem.
http://www.flickr.com/photos/sndsgood/   https://www.facebook.com/#!/Square1Photography
 
i agree  make them  replace   ur @!#$ and fix it if not do it urself  either way