97 Civic, tachometer jumps up

My daughter's 97 Civic had its engine replaced recently. Today, as the car went over bumps she saw a light blinking. She thinks it's the check engine
At the same time, the tachometer would jump 500 or more RPMs, but she didn't notice the engine increasing in acceleration. I drove the car myself and, as I saw the tachometer increase by 500 to 1000 RPMs, I heard a noise twice. Not big nor long, but as if something was grinding against something. I didn't notice the engine increase in RPMs either.
Any idea what this may be?
Than you

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