I checked the one I have it it's expired as well. They emailed me the coupon after I had spent a lot of time shopping car audio (speakers and head units) on the amazon site. You should make sure you are signed in under your account so they might send you special offers.
Also check your "gold box" deals in your account, they still send offers based on my shopping history, and some are good deals. Look at the little treasure chest icon when you log on.
Might help, good luck on the deal search.