Funny noise on cold start up.

Funny noise on cold start up.When I start my 2003 expedition I hear a nosie almost like a gurgle or rumble. It sounds like its under the vehicle or exhaust realated. After I have been driving and I cut it off and cut it back on it won't do it. If the truck is cut off for 5 to 10 minutes it does it again. My father-in-law said its just the tail pipe rattling.It sounds like something might be wrong to me.(5.4l engine 2003 eddie bauer)