As I've read in several books on worship (see below), the basis for this belief goes back to the roots of various kinds of music in African tribal music. The reasoning goes that since the tribal music was demonic (by intention), therefore its successors must have a demonic back-beat.
However, I once read a senior thesis by a student at New St. Andrews College, in Moscow, Idaho, USA, that had a powerful argument against this line of reasoning. Alas, I do not have access to the thesis. She argued against the line of reasoning on various biblical bases.
We have virtually no idea how the Psalms were originally sung. We certainly do not have any original tunes, and we have very little idea of instrumentation. Again, that is simply something I have read in books (a few mentioned below).
On a more general worship/music note, I've found the book All God's Children and Blue Suede Shoes, by Ken Myers, to be extraordinarily helpful, as well as Why Johnny Can't Sing Hymns, by T. David Gordon, and Reaching Out Without Dumbing Down, by Marva Dawn.