I just replaced my original 508 with another unit. The 1st unit had a whinning whistle kind of sound. The 2nd unit is quieter but still has kind of a low hum. To me this is not acceptable. The units I have heard in show rooms like Circuit City, my local dish vendor are very quiet. Do I have another defective unit or is this an accepted noise level with pvrs? If I choose to keep the unit, do I just have to get used to the noise??????????