Shirring noise when car accelerates

I have a 1998 Civic EX Coupe, manual. Frequently, when the car accelerates, I hear a loud metal shirring noise. I have taken it to the dealer about this issue, but they find nothing wrong with the car and do not hear the noise when they test drive it. Do you have any suggestions? Thanks.

any other way you can describe this sound? When does it occur? Is it a ticking noise, a scraping noise? does the noise change when you change speeds? when you turn? when you brake?

If possible, you drive the car while the mechanic rides with you. Point out the noise when you notice it. If you have a phone with record capability, try capturing the sound on it so you can replay it for the mechanic. I suspect that the Civic may have a loose heat shield on the exhaust system that is resonating at a certain speed and power setting.