This is not directly answering your question, but I will throw in my opinion that noise cancel/channel management on the E-Trac is extremely important. I noise cancel at least 30 times during a normal hunt, maybe 50 times or more at a difficult site. I've proven (at least to myself), that this matters, and matters alot, in the field. I can't count the number of times I've gotten an iffy signal, noise canceled, and then the target blew my ears off. That, to me, says it matters. Beyond that, lots of experimentation on my part proves that it matters alot, and has allowed be to develop a system of channel management to optimize my odds of success.
I've written an article on the subject, but since its on my web site (which is commercial), it will vanish if I post a link. So google around, and see what people have to say about the importance of noise cancel on the E-Trac (Minelab has some good blogs, for example), but the best education is to play with it in the field yourself rather than believe what others say. (Its importance, for example, may vary by location).
BTW, my recommendation is to noise cancel with the coil on the ground, not 12 inches in the air as the manual recommends. Take it FWIW, and experiment at your own sites. A day does not go by that I don't experiment with noise cancel at each new site.
HTH