On Thu, 11 Oct 2018 09:07:36 +0200, Emanuel Berg
wrote:

On my racer, there is a wire under the
top tube. On this wire hangs three very small
plastic washers. Unless someone forgot to
remove them, the only thing I can think of is
they are there to prevent the wire from
rattling against the tube. Not that that would
happen very often for a stiff wire, right?

You'd be surprised. I bought a new (second hand) bike that had the
rear brake cable run from the brake lever to the rear brake in the
cable housing with two tiny little metal clamps to hold it to the top
tube, The first time I rode it on the road there was this funny little
"ding, ding" every time I hit a rough place in the pavement. I stopped
twice to check and couldn't find anything loose. Later I was doing
some work on the bike and dropped the bike about a foot (onto the
tires) and "ding, ding". It was the center section of the cable
banging against the underside of the top tube. A third clamp at the
middle of the cable stopped the noise.
--

Cheers,

John B.