We had one of those annoying noises in the house for awhile too. It drove me crazy. My DH is hard of hearing (all those years flying jets) and he just couldn't hear it. I thought it was my GPS, low battery. Nope. Then I thought it was his cell phone, low battery, nope. Not the smoke alarm, not the laptop low battery. Just couldn't figure it out for months.

Then all of a sudden one day, bingo! I was in the laundry room and there was the sound! It was the dryer! Something was rubbing inside the drum! So, I got that fixed!