I purchased a 1992 NSX with 157k (161k now) last week and drove it cross country from California to Virginia. It was fine until I reached Indianapolis, Indiana. From there, I heard this slight knocking sound (like knocking a door) when I accelerate. It's noticeable in 1st, 2nd, and 3rd. Once cruising, there is no knocking. There is no knocking when I brake. At first I thought it was the muffler hitting against something but it's not. I looked underneath and did not see any leaks. Has anyone else run into this problem? I'll take a closer look into it this weekend.