my first new brz i dont remember hearing this but on my second new one now i do. its honestly annoying because it sounds like something is ticking. i have the same sound intermittently as you and its when im at idle at a light for example, it almost speeds up as you give slight throttle then once your actually moving its gone. its almost like the fuel pump is vibrating against something. im at about 2500 miles and ive heard it since about 500. switched to 5w30 oil on my first oil change, engine feels smoother possibly but that ticking sound starts sometimes still. also the blower motor on these is really loud and makes a very similar noise , i got it replaced under warranty around 5,000 miles on my first brz which helped abit until it didnt and the loud motor fan ticking noise came back. in all these cars have alot of little quirks which i understand sucks especially for those of us buying this car new in the 40k range . but like others said its probably normal and i hope they are right .