iPad not charging- switching between connected and not connected
I have an iPad 3 I think. Normally when I plug it into its regular wall charger with the 30pin cable I get a ping sound letting me know it's connected. Then the icon switches from battery to the lightning bolt indicating a connection to the wall. In other words, it's charging. But now when I plug it in I get the ping sound, followed by another ping sound telling me it's not connected and then connected again "ping" not connected, connected again "ping", etc. Over and over again. The connection lasts less than 5 seconds and then reconnects with another ping sound.
Nothing about the USB 30 pin cable seems to be a problem.
Why is it doing this? How can I fix it so that it charges from the wall?
Thanks
iPad, iOS 9.1