[Lucky]

If the noise is for a few seconds at start up, that's normal. I'd suggest running a 5w40 oil (versus the widely used Mobil 1 0w40)... it will result in less rattling at start up.

The term "pre-lube" usually refers to a system that builds oil pressure before you turn the ignition key to start the engine. This is common practice on race cars since their engines are often built to very tight tolerances and are usually filled with a thick oil which offers maximum protection at high loads, so significant wear would occur at start up before oil would circulate and build pressure.

However, I don't think your mechanic has the above in mind. More likely he is suggesting that an aggressive cleaner be put in the oil and the engine run for a few minutes before draining and refilling with fresh oil. There are many such "engine cleaners" on the market.

By the way, I can think of a really good way to clarify what your mechanic is suggesting: ASK HIM! I'm sure he'd be happy to explain what he has in mind.