I found a few threads on possible exhaust leaks, but most terminate with a joke or being chocked up to valve train noise.

Here's my issue: Finally was able to take the car out after months of wet streets and snow. The streets were clean and dry after large amounts of rain (to wash the salt away). Any way, after flogging it for a while to clean out some carbon , I did my usual inspection. The typically noisy valve train is still there, but so is a louder, more imposing tick. I opened the hood and all sounds normal (for this engine). Valves and injectors tapping away, but under the car on the passenger side, there is a distinct tick that is in time with engine RPM. It is definitely on the driver's side and is not distinguishable from the engine compartment, but is very noticeable when listening from under the car, near the engine. It sounds kind of tinny or metalic, but I've heard exhaust leaks that sound similar depending on the thickness of the piping. I can't pinpoint the exact location however. So, I'm hoping it isn't a lifter banging or other engine component. Could this possibly be an exhaust leak at the header collector flange? Is this a normal sound for this German sewing machine, or...? The car has about 13k on the clock. To my knowledge, it's never been bottomed out on anything. I've spent a ton of time under the car inspecting things. No scrapes or similar markings. I've had it checked out by the service department, but of course, everything sounds normal to us, bla, bla, bla.

Thanks for any suggestions or advice!