When I turn the ignition key, I hear a high pitch scratching sound, before the engine turns over and I don’t hear the noise anymore. This happens intermittantly.
One of two things…
either you’re holding the key turned too long after the engine cranks over
or, your starter is gone bad. The starters on the Sentra sounds like you stuck a pen in the running blades of a fan after the engine kicks over. I had this problem on my 96 Sentra. Brand new starter cleared it up. Something also to check is if the starter has come loose. This, i’ve heard, is a common problem with the Sentra. The torque from the starter manages to work itself loose from the engine body.