knock at startup
My 96 t-bird did that when I first got it...I couldnt ever figure out what it was caused by, and it would only do it after the car sat all night...I changed the battery a couple months after I got it, and not only did the car fire right up a lot quicker then before, but the startup knock was gone, and never re-appeared for the rest of the time I owned the car. Could it have been the starter due to the engine not turning over very quickly due to a almost dead battery? Possibly, but I'm not sure...Try a fresh battery, worked for me.
Hope this helps
2015 Mustang GT Premium / Manual / 3.55 / Recaro