Tapping underneath while braking/pitched?

Hey guys, this seems so simple, since it can really only be a couple of things, but since I need to be moving to replicate it, and I'm not familiar enough with the underneath of an XJ to know what's good and what's bad, I need some suggestions.

When I brake and the Jeep pitches forward, I can hear a tapping of something rotational underneath me, maybe just under the firewall that slows and stops with the car. I assumed driveshaft, but I can't see anything it would obviously be hitting. It also happens briefly after a bump in the road. Is this still probably the driveshaft and I'm missing something? Exhaust maybe? I had the exhaust detached from the head for a good three weeks while I was swapping the head, so maybe it's not aligned correctly?

Just wondering if this is a FAQ that there might be an easy answer to. Thanks all.