This is how it should be, this is the way how you're volume
control is build in you're pre-amp it sounds a little like high pithsing (wistle like) sound.
Check with you're Mark Levinson dealer, and let me now.
The T2 from Treshold has when you turn the volume loud klicking sound this is also the way its buid.
By the way a ML380s does not have a pot meter!!!!
Alex