iPhone 6 charging problem
Sounds like a bad cable / USB adapter / power outlet. Maybe lint on the Lightning socket.

Does the battery icon alternate between charging / standby or anything else on the screen change with the tempo of the sounds?

Three things are needed to charge:


USB power adapter 
USB to lightning cable
Phone internals / charge circuitry working correctly


It's probably easiest to plug the cable and phone into any other USB charger or USB hub or USB computer. If the problem follows the cable or the phone - you'll need a different phone or a different cable to know what's faulty.

Worst case, put the phone in airplane mode (or power it off) and you'll hardly lose any change over night. It won't top off, but you can take it to another charger/cable in the morning or find another phone to test with your charger and cable.