Everyone has given you great ideas for troubleshooting. One other thought: If you mounted the cartridge yourself, as I did last January, and hear God-awful distortion as you describe, as I also did last January, and nothing is wrong w/your phono pre or settings, then you may have badly misaligned your cartridge--as I did last January. I thought I had done a good job, then I played a record and had to run to take the arm off the platter! Before I did, I saw that the bottom of the cartridge was actually touching, in fact dragging, along the surface of the LP. Needless to say, this sounded hideous and created unbelievable distortion amplified excruciatingly through the chain to the speakers.
Duh! I had to start over w/cartridge mounting 101.
Duh! I had to start over w/cartridge mounting 101.