2004 Subaru Outback rattling

I brought my perfectly fine car in for new tires. While there, the mechanic told me the serpintine belt needed replacing. So I received 2 new tires, an oil change, a new serpintine belt and had the tires rotated.

Within a day, my car developed a rattling noise coming from the front of the car. It happens when I turn the wheels to the left or accelerate up a hill. I took it back to the mechanic who said the heat shield clamps were corroded and loose so he tightened them and said if it keeps happening he would remove the heat sheild. The car stopped rattling for a few days, but started again. It also doesn't rattle every time I turn or accelerate.

Does this have something to do with either the new belt or the tire rotation? Could it be a "heat shield rattling" and if so, don't I need that? I have no faith in this mechanic as I never used him before and my car was fine until he touched it. Any advise on where to send the new mechanic looking?