Out on our 20 mile daily tandem toot today when there was a sudden noise from back wheel: 'clang, clang'; applied both brakes and got a 'scrape, scrape' noise too. Switched to front brake only, stopped and checked back wheel.
A piece of wire about 18 inches long was wedged between right rear brakepad and rim and created the 'scrape' noise when we applied brake; 'clang' noise was the wire hitting the spokes.
Yanked wire out and readjusted rear brake a bit and we were on the way.
Several years ago we had a similar experience with worse results. Got 'clang clang' noise from back of tandem, shifted rear derailleur and got qiuet, then, got worse. Checked back wheel and had a chunk of wire wrapped into the cassette and chain. Messed up the cassette and eventually the hub.
So beware of gettin' wired!