Sounds like the opening of Schubert's 5th Symphony.  May I recommend the
following site:

   http://melodyhound.com/

Here you can reduce your Ohrwurm to a sequence of U D R - for up, down,
repeat and match it to a melody in their database.  The site has the
Schubert melody, though not enough of it to distinguish it from many
other tunes.  I think I found out about it from this list.

Virginia Knight
Personal homepage: http://www.ilrt.bris.ac.uk/~ggvhk/virginia.html
Blog (mostly about singing): http://edward.ilrt.bris.ac.uk/~cmvhk/blog/