I really hope someone can help me.

After a power outage my S750's stopped working. I thought it was the fuse, so I bought new ones and replaced it, but it didn't work.

It took me a while to find a place that can repair speakers and they told me the IC's blew up etc etc... I was excited it was gonna get fixed.

After a week or so I got my speakers back and they did work. But there was a problem... I don't know how to explain it so I asked around and a few people told me the term is "humming". Forgive me if its the wrong term, but this is what happens... there is a high pitched annoying sound that comes from the sub-woofer. After the repair it continued for around 20 to 30 mins and stopped. I thought it was fine then, but the next day I switched it on again and the sound was back... again for 20 to 30 mins. I've noticed that if i keep the sub-woofer on the annoying sound stops but when I switch it off for a few hours it comes back for 20 to 30 mins.

Can somebody please tell me what the problem is and how it can be fixed?

Any help from this community will be much appreciated.

Thank you in advance.

Looking forward to some positive replies.