iPad continuous beeping sound when plugged into Mac

Original Thread:

"When back up my iPad to my iMac, I get a continuous beeping sound showing charging/not charging. Why is this happening? It does not do it while plugged into the wall. Only when plugged into iMac. iTunes not recognizing device."

Had exactly the same problem, reason: incorrect specification cable (don't ask what the spec should be!) Fixed it by using an extremely good quality connection cable between the iPad & MacBook Air.