I have a Tempstar high efficiency gas furnace.  Just lately when it
starts up I have noticed it seems alot louder than I recall. This is
running it in the heat mode.Any idea why?

I am a heating and cooling service technician and have worked on
plenty of these and our number one complaint for noise would be the
ventor motor..which is the black motor hooked up to the pvc venting to
the outside ... however to replace it it is pretty high priced...I
would hang on to the noise as long as you can unless the unit is under
5 years then it will be under warranty..good luck