I took my car out for a drive today after it had sat for several days and been rained on quite a bit. As I started driving I noticed that the exhaust sounded kind of buzzy between 1.5-2K RPM or so, but once the engine started to warm up it went away and didn't return. Is this something I should be worried about or should I just put it down to the engine being cold and having sat for a few days?

 

It was due only to condensation in the exhaust pipe, which evaporated once the hot engine gasses passed on through.