2008 Subaru Impreza Smell & Noises

I know you cannot diagnose noise or smell online,
but maybe you can help me out!

I just bought a 2008 Subaru WRX I am getting back to driving a manual after my MB C230 Kompressor. It has been several years. I think I have been rough on the clutch but getting better, I am okay with the clutch and doing fine now, but I notice when I accelerate and shift gears I hear a "pop" (little and quick noise but only when I accelerate, not when I down shift. It comes and goes. Also there is this burning smell that I smell only after I take off if my car has sat for a few hours. I run Premium fuel and I put Marvel Mystery oil in as well. (Always use the stuff) wonder if that could be it. I am not a gear head so basic understanding would be nice.