Should I lubricate the motor in my power drill?
The drill you display is for DIY use (as opposed to professional use), so it's designed to be durable enough for years of typical DIY usage. So it has no user-serviceable parts - even its brushes will last for about one hundred hours of motor running and you're not expected to think of what happens to them after that one hundred hours.

That's why you really have two options - either just continue using it or bring it to a service center and prepare to pay a fortune for servicing.

One possible reason of noise is that after mild (thus permissible) wear accumulation it just started to sound differently.