When I started up yesterday for about 3 seconds I heard a metallic tapping sound from the engine. Cold engine, had sat for about 9 hours. Temp at the time was about 75 degrees outside. Never heard this before. I have had it for about 3 months and runs very smooth has about 114000 miles. 2004 X, L6 engine, automatic. Any idea what this might indicate or what work I should get prepared to have done and when?