Rattle / grinding under acceleration

I have a 14 FiST with 44k on it, just recently noticed in the last month that it has alot of rattling coming from up front under acceleration esp below 4k rpm. Also i get an odd sound almost like a grind/rub combined only under power and its very noticeable esp in lower gears. The car does not make any of the sounds at idle or under coasting that i have ever heard. This is the 2nd transmission in my car (replaced at 32k) and when i did receive this trans it has a funky 2nd gear in that caused my shifter and arm to vibrate and shake violently for about 800 miles after receiving it. I had taken it back to the dealer and the manager felt it but since it didnt do it every single time about one in every 3 shifts into the gear he said there was nothing they could trouble shoot since it was wasnt repeatable every time which is BS to me. The vibration is still there though the violent shake slowly faded over time so w/e was causing it must of worn down...The only thing that has been changed was brakes and rotors that i did but the sounds and rattling didnt occur till atleast a month after that was done and i have since double checked all bolts etc associated. I am hesitant to take it to a dealer at this point after all the issues I have had with this car and the run around i was given as i have no desire to pay for rental cars or dealer fee's now that the main warranty is up and only the drive/power train warranty is applied. I had to get a regional service rep involved last time and I have a feeling i will this time as well.