What is the basis for why certain musical beats are deemed by some to be unchristian or immoral? I have encountered people in the past that have asserted that certain musical rhythms or beats are inherently immoral or sinful.  

It seems to follow, then, that even if the words of Scriptures themselves are put to music with the wrong beat, the result is somehow still immoral.

What is the particular basis or argument for this belief?  Is there any biblical basis for this?  Did the Psalms follow a certain beat pattern that could be the basis for this thinking?
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.