No sound out of speaker module!

I have a iPhone 4s with no sound coming out of the speaker module, i replaced the speaker module and the dock connector flex, and get sound out of the speaker module intermediately for 2 minutes then it goes off i tried a factory restore and hard reset no go, i tried a different speaker module and a different dock connector other than the one i replaced it with and still the same works for 2 min then stops, when i power off the device and turn it back on, the sound does not work at all until i take out the speaker module and put it back in for only 2 min?,

Anyone's help would be greatly appreciated,

Thanks,

Chuck