It usually doesn't get bad until I have been using it for a while. I guess it would be ok to let it idle at 1500 for 30 minutes or so?
I would say that would be fine. Keep an eye on the temperature. Not all engines cool well at idle. But I'm curious why you would even be concerned with idling for half an hour?? That should make no difference to the engine at all.
BTW, nice of them to say that they would fix whatever if it goes wrong? I like people who deal that way. Although that is counting on their memory of the conversation. Do you think they will remember saying that?
OK, now to mechanical stuff:
With most things engine-wise, noisy parts get quieter as the parts heat up and clearances get to normal running values. An exception to that would be valve to rocker arm (also called tappet) clearance noise - which can increase as the temperature rises, particularly at higher RPM. Too much valve clearance makes noise but is not an immediate failure indication, simply a notice that it should be adjusted.
That is not a difficult job. Any old-time mechanic can do it for you. Today on cars it is rarely done, but on diesels and industrial engines it is a normal maintence item. I admit it is an item which is often ignored because it rarely changes after breakin of 50/100 hrs. And also because having a valve clearance a few "thou" out of spec is where that valve "wants to be" and in my experience better left alone anyway. But that wouldn't make noise.
What a mechanic would do is take off the valve cover - having on hand first a new gasket in case of need. BTW, you should have that gasket anyway. Taking off the cover is a matter of only a few bolts at the very top of the engine & easy to do. Then he will rotate the engine slowly by hand via a socket on the front of the crankshat nose while looking at, feeling, and possibly measuring the valve to rocker arm clearance as the valves open and close. He would be looking for something obviously way out of spec. Probably double the normal clearance. Easy to see and feel. Having one valve way out isn't unusual on a new engine because of the way valves settle into their sockets, & is easy to see. Anything even roughly close +/- 20% of normal clearance is not going to make that much noise.
Then he will pull the dash lever while watching to confirm that the compression release - if yours has a compression release -is operating properly and not a source of rattle. They often are because the spring which holds the compression release away from the tappet is not tensioned right. He would then set the clearance on anything that is way out of spec, and put the cover back on. It's an easy job. You can do it yourself if you'd rather. Every shop manual tells how. Tools needed are very basic.
rScotty
