I have an IDEA about what may be causing this issue (channel imbalance).
I used to work as an IT and the company CEO insisted on wearing polyester shirts. His (expensive) laptop
kept crashing, and eventually required a new hard drive. This happened 4 times in less than 12 months,and
to 3 new machines. Eventually the only thing left was STATIC DISCHARGE from his clothing to his laptop casework.
The problem went away once he started wearing cotton mix shirts.
So, anyone having a channel imbalance with the 009s or other Stax headphones, it may be worth looking at this.
I know from swopping out PC chip sets, I had to wear an earthing strap around my wrist. And some folk do carry
around more static than others. Some cars can get static build up as well.
This would also explain why storing the 009s for a week fixes the issue (for a while), as they would then discharge.
Remember, laptops running of a battery cannot discharge static away down the main cable. Also units mounted
on wooden shelves or glass shelves likewise.
Something to consider you guys?