James,
I would recommend that you borrow or purchase a good quality MONO recording and try changing your volume while it is playing, as you described above. Stereo can create the effect you describe just due to the nature of the recording. Also, I recommend you purchase the Cardas Frequency Sweep record. It has many tracks dedicated to trouble shooting and will degauss your cartridge and clean the stylus as well.
I would recommend that you borrow or purchase a good quality MONO recording and try changing your volume while it is playing, as you described above. Stereo can create the effect you describe just due to the nature of the recording. Also, I recommend you purchase the Cardas Frequency Sweep record. It has many tracks dedicated to trouble shooting and will degauss your cartridge and clean the stylus as well.