if its fan noise then it could be from the gfx, the cpu or the psu. they all have fans. the hotter the system gets the harder the fans work.
the base of the problem is likley to lie with the case. as you only have 1 front induction fan on the front and maybe 1 on the side but you have 5 potential exhaust fans. meaning your case will be starved of air so wont cool effectively.
this then leads to higher internal fan speeds as everything fights for the limited air that is there... leaving the side panel off will help in 1 respect. your system wont have a negative preasure and the fans will be able to draw the air they need. but the rest of the components wont get cooled effectivley as there will be little overall movement of air around the case. closing the case will resolve this...
in the short term you can turn of 1 or 2 of the extractor fans at the top of the case. and maybe move a fan from the top to the bottom next to the psu if you can, and set it to intake.
leaving 1 at the top and 1 at the back to exhaust the whole system. over all this should ballance the air flow and help reduce noise.