I have a Sonic Impact i-F2 Speaker Deck which began buzzing when plugged in with the AC adapter. It stops buzzing when just running on battery. Problem is, I mostly listen to the deck at home and keep it plugged in. It did not always buzz on AC adapter. And the unit was not abused, dropped or got wet, etc. It's several years old, but I did not expect it to simply "wear out". Can you cite a solution? I really like the deck. Thank you.