I've been reworking my exhaust, and I had my rear (downstream) o2 sensors unhooked for a few days. This disabled the eco mode as well. I noticed that the entire time the sensors were unhooked, there was no hemi tic. Now that extensions are installed, and the eco mode is enabled again, the tic is back. I've gotten accustomed to it now, but if it annoys anyone and they want to do some figuring out, this may be useful info.