I read that SSD has a lower noise level than HDD because there is no spinning mechanical reader. However, if I have a hybrid laptop with SSD and HDD, will I notice any difference in overall noise level of the laptop? In addition, how significant is HDD noise compared to noise from other sources in the laptop, i.e. GPU, CPU, fan?
The tiny amount of SSD supplements the platter drive, but does not replace it. Most of the noise comes from the spinning of the platter motor and not in fact from the heads sweeping across the platters, so sound will be reduced very little.
The biggest source of noise in a laptop is any optical drive (when in use), followed by fans, and then any platter drive follows far behind both. Electromagnetic components (transformers, inductors, etc.) make a tiny bit of noise, but the solid-state electronics in a laptop do not make much noise at all (usually <5dB).