Lenovo Y520 noisy fans

Lacking a good bit of information but can tell you what to look for. If noise is when fans spin up it can push 40db of sound which is quite noticeable but if the spin up of rpm is happening when just sitting idle you have cooling issue. My new yoga 720 had poorly done thermal paste and 2 thermal pads not even on the components. Had too open, remove heatsink and fans, redo it all and hardly revs up even under load much lower rpm needed. If sound is like ticking noise which varies with rpm something like a wire is interfering with the fan blades. Not knowing more details like fan type (mine are the new metal ones-less flex/more efficient) it is hard to pin point root causes. I did not notice any software controls for my fans and the thermal sensors seem to be bios controlled which there are no options to adjust. So, if brave open up and look it over carefully. If like yoga going to need a torx number 5 to remove bottom cover. My local hardware store sells a sweet kit for 20$ to work on electronics like cell phones and laptops. Had full set of torx in small sizes and plastic separator tools, suction cups and more that came in handy. Next need some thermal paste. Look on web for how to and which, I use silver 5 but have experience using it (it is conductive so newbies should use porcelain based thermal paste) A web search should result in maintance manual pdf for your system which has full instructions on servicing the unit. Good luck.