Ticking from oilpan and transmission

I have a 1998 Blazer, that has a tick sound coming from the oilpan trans. area, i used a hose to hear where it was coming from and its right were the trans and oilpan is bolted together. it tick loud at idle and goes away when you get on the highway. Any ideas what this could be?
Thanks

i had that ticking on my 97 .... turned out to be a cracked flywheel. id remove the inspection cover and take a thorough look

thanks for the help, i will check that out