Help needed to diagnose preamp channel unbalance.

Hello all. The preamp is a new dual mono linestage with both balanced and single-ended connections. The volume control is an Alps motorized pot. There is no balance control, just a single stereo volume control.

The problem is that at low volumes, there is a channel mismatch resulting in the right channel being noticeably louder than the left. The problem was confirmed to be with the preamp through cable/channel swapping and listening with matched channel test CD's. Correct phase was also confirmed. When the volume is increased to moderate levels, the left channel seems to come fully on-line so that proper balance is restored. This is obviously an unacceptable situation for low level listening.

Has anyone had a similar problem? Is this likely a tracking problem with the volume pot? Is it possible this will improve as the electrical components and volume pot break in, since the preamp is new with only about 15 hours on it? - Thanks