I have a 2012 Altima that makes a kind of  grinding noise. I know this sounds odd but I always compare the noise to if you had something vibrate against an empty can (that’s the best I can describe it as) BUT the noise seems to only happen at 2.25 RPMS I have taken this problem to the dealer for them to say the issue could be several things (so I got a few things fixed they suggested I needed, and I paid $2k in repairs for it to be fixed with no luck the noise was still there)  I took it back and they swear they cannot identify the issue and that I shouldn’t worry. But the noise is persisting and gets worse over time, any suggestions or ideas?