Speaker keeps cutting out.

Speaker problems.  I recently took an older Alpine stereo out and replaced it with a Alpine 9857.  The previous installation was done by the shop where it was purchased.  It's in a Dodge Grand Caravan.  It has two speakers in the dash, two in the doors, two in the rear and one sub woofer. Along with a modest amp. With the old head unit I was told that the drivers side rear was blown.  It did have all the signs of a blown speaker.  So I replaced it.  This new speaker did the same thing.  So when I put the new 9857 in I thought it would solve my problems.  Still did it.  I even took it to a different shop.  They checked the old blown speaker and it worked.  It doesn't do it all the time though.  If I turn the volume up for just a bit the speaker starts to work again. Then the next song it starts again. The technician came to the conclusion that my amp might be the problem.    When I took out the speaker I did notice that this is the speaker where they spliced in the sub woofer.  Isn't there some kind of crossover or capacitor that they used to mover the low bass to the sub woofer?  It's a big taped up connection. Could this have gone bad?  I really don't turn this stereo up to where it's going to blow speakers.  How can a six year old amp go bad?
Thanks for your help.