The left side of my exhaust manifold turns brown similar to rust color. The right side is still color gray. I can also hear a sound similar to fan hitting something when pressing the accelerator. It's coming from left side manifold. I tried raising the vehicle with lifter to check if there is a leak. Can't find a leak, I'm not sure if the sound is coming from the manifold or catalytic converter.

 

What year?

Newer trucks have some small ticks from cam phasers, nothing very serious. Since the passenger bank usually contains more heat than the drivers side its a little confusing how the left side faded first.

 

yea what year..my 2002 still has a "tick" but i just had all the exhaust leaks sealed up...finally...and felt around and couldnt feel anything..i know its coming from the top side, pretty sure its not the exhaust manifold so im not sure what it could be

 

2000 E150

I have a leak in the left side manifold.