Ticking Sound

You know we can't hear it so we can't offer a diagnosis, but I can offer some suggestions. First of all some hydraulic lifters and lash adjusters can take a long time to pump up after an oil change. I had one that always took 30 miles, then it remained quiet until the next oil change. Second, if one mechanic didn't hear anything abnormal while you did gear it, you are likely hearing a normal noise. Injectors do make a rather loud ticking sound but you typically won't hear them from inside the car. You can buy an inexpensive stethoscope for yourself from Harbor Freight Tools or any auto parts store, then listen to them yourself, but it's hard to say if that's what you're hearing now. You WILL hear the injectors with a stethoscope.

You may be able to identify the injectors as NOT what you're hearing, particularly if you can hear it inside the car with the hood closed. If you're hearing a slower and louder sound than the injectors and it doesn't occur all the time and it doesn't change with engine speed, look for an emissions solenoid that thumps on and off. Those can be covered with foam silencer pads.

There's also a tool you might be able to borrow from an auto parts store that rents or borrows tools called the Chassis Ear. I won't go into details now because it is used for locating squeaks, rattles, and other noises that require the car to be moving. You shouldn't need that if you can hear the noise now.