The nosie in the headphones is a common problem with electrostatic headphones. Overtime, the dust or moisture could evetually find their way into the driver. Fixing this problem isn't that easy, unfortunately.
You never, ever want to clean the diaphragm with alcohol or acetone. If you do that you'll wipe out the coating material on the diaphragm. You'll end up destroying it.
Try to clean the stators as best as you can. If you see some dust on the diaphragm, you can try blowing it off or use a small brush to gently wipe it off.