Can you figure out what side it's on?
Then isolate if it's front or back?
Not that either of those things matter for what I'm gonna suggest here...
If you torqued the injector hold downs to the recommended spec of 22ft lbs, you might have pushed an injector...
I just had this problem after my engine install, freaked me the hell out too!
Lol
Once I realized what was goin on, I just tightened the hold down bolts with the truck running and they sealed and the noises disappeared! I found it really quick tho, if yours has more than a few miles since the repairs you might have to pull the injectors and replace the copper crush washers and o-rings.
FWIW
I was able to reach all the bolts through the wheel wells, it's a 12mm