I recently had some repairs done to the car

I recently had some repairs done to the car. I had a timing belt replaced, and a valve cover replaced.

When running the engine, whether idle or driving I hear a noise. It sounds like the pulleys moving a belt. It's very subtle in idle, and at low speeds it's a lot more noticeable. Mechanic said Timing Belt needs to wear in, and that's the noise I'm hearing. I've had it replaced previously and this noise was not present. Is this plausible?

The vehicle also was smoking, and smells like oil. This was not there previously, and mechanic stated it's probably because he disturbed things in replacing the valve cover. There is also oil all over the front of the engine that was not there previously. He states he can not find any leaks. Could this oil be from the valve cover replacement, and the smoking all related?