UPDATE 3: just got back from test driving the new Toyota 86 with an automatic transmission and it has the same noise during the same rpm range. The tech explained the noise is common as it comes from the engine. Also, on rough surfaces, the new 86 has interior rattles as well. In conclusion, i have sought comfort from the fact that another new 86 has basically a similar characteristic in terms of nosies and I am much happier that there is nothing wrong with my car. I guess I can start enjoying my ride now. It's in red
last but not the least, I would like to thank everyone for their attention of either simply viewing or replying to my post. I wish you all have a nice week!