I have an '05 Ext Cab Silverado Z-71 that I just bought about a month ago. The other day I was hauling a load of landscaping block from Lowes (about 1500 lbs worth) and I noticed a pulsing squeak that would become more frequent the faster I went. It only happens while accelerating and not when cruising. Almost as if the exhaust is rubbing on something when the engine is under load and torqued over to one side. I figured that maybe with the load in the bed that maybe an exhaust hanger or something was rubbing on the under carriage and that once I unloaded the truck it would go away. Well, it didn't. Now it's getting louder by the day. I climbed under neath to take a look but couldn't find anything. I've pushed and pulled on about everything under the truck and can't seem to replicate the sound. Any ideas before I go to the dealer?