My subwoofer makes a very loud shreaking sound consisting of a mixture of high and low tones (almost sounds like it is about to explode) after power has been on for about 5 minutes. I had the problem before and sent the speaker away for repair. I was told the driver(s) needed to be replaced. The repairs were apparently done but the problem is still there
Audio Players & Recorders - Wharfedale - PowerCube PC-10 Subwoofer
Answers & Comments
Did they charge you much for that 'fix'?
Though it may have become damaged in the original problem, the driver won't make loud sounds by itself in the absence of a signal. The internal amp is probably malfunctioning and it is very capable of destroying its own driver. Don't let it continue when it starts acting up.
Did it work correctly for more than 5 minutes after the driver replacement? Take it back and make them do it right this time.
I had a powered sub amp problem that the local guy couldn't fix so I just disconnected it and wired the driver directly out to a separate amp. Works fine as a passive sub.