I have a ticking noise when the van accelerates. Mechanic states no exhaust leak on 1996 Ford E-350

No warning lights, no definitive codes

Asked by for the 1996 Ford E-350
And the engine is
5.8L Sounds smooth, just ticks louder as it accelerates, bu not rough
What else did the mechanic think it was, or did he hear it? Reason i ask is, that is exactly what an exhaust manifold leak @ the cyl. head would sound like!
Does it get quieter as the engine warms up?
I initally asked about a manifold leak. He mentioned it may be an 'erg tube' but he would have totake it apart to see what it was. He said the manifold's' were OK, but it may be 'one tube or the other'. It is quieter at cruising speed
2 more answers , 1 more comment
Stupid question.......Is the 'ticking' happenning when the VAN accelerates or when the ENGINE accelerates?.poss.driveline issue?
Made me think,but it definitely is when I'm steping on the gas pedal, not when the van is moving forward.
smog pump needs to be changed or broken loose