Strange engine noise

[405landlord]

I have a 2003 Suburban K2500 with 6.0 engine. The other day it suddenly started making a loud "flapping" noise when I would accelerate. The noise was not there at idle but would get very loud from 1500-2500 rpms. It started this about 5 miles from home and continued until I was about 1 mile from home when it suddenly stopped. Just like someone threw a switch. Can someone help with this? I know if I take it to the dealer they will say that they can't duplicate the noise so they can't fix it.

 

Thanks.

[71GMC_3/4T]

Check your serpentine belt for a bad spot.

[budhayes3]

Is the noise still there? Maybe something got stuck in your undercarriage (plastic bag, angry old bag, etc.) and worked it's way out.

 

P.S. Welcome!