There are a number of ways to get rid of a second mortgage. You can settle for pennies on the dollar, or you can get rid of the whole amount in bankruptcy. Alternatively, you could negotiate a modification of the loan. There may be an assignment of the deed of trust in the public records which indicates the current noteholder. Alternatively, you can request the identity of the noteholder from the servicer, Green Tree. In any case, you don't need to know the identity of the noteholder to get rid of it. Green Tree is your point of contact.
If you simply stop paying, the holder of your second may foreclose. It could do so now, which would make sense only if it bought out the holder of your first, or it could wait until you paid off your first. It could also just wait until you sold or refinanced the property, at which point you would have to pay it off.
I agree with Mr. Gramham. My two cents is this: I have known some homeowners whose home is extremely "underwater" do nothing--includle not pay the 2nd mortgage. In some instances, I have known the second lien-hold to "forgive" the debt because they realize they have no practical basis to foreclose on the homeowner, e.g. the second lender would get nothing because there would not be enough even to pay the balance of the first loan--thus, zero incentive to pay for the foreclosure-related fees. In other words, some folks have considered a "wait an see" approach as an option.
PLEASE READ--before emailing, commenting or calling: As a rule, I do not respond to "comments" that are designed as follow-up questions to the originally-posted question. I specifically do this as to avoid creating any confusion to the originating author of the question and to prevent any attorney-client relationship from forming--as this is not the goal or intent of this attorney or the Avvo creators.
Further, I am only licensed to practice law in the State of California; therefore, any information provided in this answer is intended for application in California. Second, the information provided in this answer is solely intended to serve as GENERAL INFORMATION, and, at most, to serve as a catalyst for discussion between you and an attorney. Under no circumstance, is this information provided in this "Answer" intended to be construed as legal advice--and is not to be considered legal advice for any purpose. If you wish legal advice, then it is recommended that you contact a licensed attorney in your area to discuss the particulars of your case. Only by engaging in a meaningful discussion with a licensed attorney, can an attorney then provide you with legal advice.