If it's coming from a fan then the frequency should increase as the fan speeds up. You can use an app to monitor temperatures to see if that's the case. Otherwise, I suspect that it is an electronics phenomenon called "coil whine". Essentially, coil whine is the audible effect of components vibrating, especially when under high load / high power. It can sound like a whine, buzz, hum, scratching, hiss, rattle or vibration. This happens with many components, but often it's not loud enough for us to hear or at a frequency that we don't hear well. These two pages have more explanation and some tips to reduce the effect: Unfortunately, you may not be able to eliminate it to your satisfaction. Much depends upon how you use your computer, the acoustic qualities of your room, other ambient noise, etc. Coil whine can occur with brand new components. Components that were previously quiet can develop coil whine as they age. It has also been reported that certain software (usually games) that draw a specific power load can cause an inductor to vibrate at a specific frequency that is audible. I once had a Netgear router whose coil whine was particularly annoying to me. I found that the volume varied among units of the identical model. I tried two or three other units of the same model in the store, and found one that I couldn't hear. Even though they were the same model, same components and power supply, two or three of them were loudly annoying to me, but the last one was inaudible.
Hi,  I bought an Inspiron 14 Plus 7430 laptop. The laptop arrived today and just after starting I noticed a strange ticking noise. This noise is not constant but comes and goes away time to time. 
Inspiron 14 Plus 7430, strange ticking sound