The OP is fine, as long as you bring your NOA to go along with your passport, if asked about immigration status. Just be prepared for it.
Whoever said that TSA is not checking on immigration status is incorrect. Here's my recent experience from another post:
"I ran into a situation just recently (April 1) at a TSA check point (San Jose CA airport). I fly with my foreign passport because my frequent flier programs are all in maiden name. The TSA looked at my passport and asked if I had a visa. I was surprised, and the TSA checker showed me a list of countries and said "unless you are from a country on the list, you must have a valid visa in your passport." I said I was a permanent resident and showed him my PR card, which satisfied the TSA person. He used the "flash light" looking device on my PR card as shown here:
http://www.tsa.gov/what_we_do/layers/tdc/index.shtmFrom the TSA link above, it looks like the "Travel Document Checker" program has been going since mid 2007, but it was the first time this was ever mentioned to me. I flew many times in 2007, including out of San Jose with my foreign passport and was never asked for a "visa." Also, on my return flight (Las Vegas), I was not asked about a visa, and just showed my passport."
I checked online and it appears to be a pretty random thing with some airports doing it and some not. Since the OP is from a VWP country, they may not even be asked for a visa, since it's not required for US entry. But if they notice the expired K-1, it would help to have the NOA as evidence of legal status.