Whenever I power on my dell laptop, there is a low volume screeching sound heard, its quite low therefore distinctly audible only when I bring my ear closer to keyboard. Although the system is functioning quite normally. Problem occurs only when I record something through the internal mic. When I listen the recorded sound, this screeching sound now can be easily heard in the background. I've attached the sound here(don't know if its shown). Pl suggest if it's a hardware issue or something else.

Hi Aniruddh... Sounds like the internal mic is picking up a bit of interference, or maybe there is something creating a crazy magnetic occurrence somewhere near the internal mic. Doesn't sound like it's going to be an easy one to nail down unfortunately :o(

Would replacing the hardware for internal mic help, if feasible ?

I'm not sure it's feasible to be honest, sounds like quite an intricate job... perhaps it would be best to take it to a specialist.