I've had CD players last well over 10 years, but some DVD players don't seem to be quite up to that same level. Try connecting it to a different input (CD, CDR, etc...) to see if it does the same thing, and also try swapping the R & L connections. I'd also try swapping the cable out for a different one just on the off chance that it is the problem.
Now, you know that you can't get true multichannel audio with just the R & L analog connection right? Do the player and preamp have digital connections?