Strange sound after I installed an oil pressure sender

[Dewster]

I re-installed the oil pressure sender in my '90 Sierra to get rid of the aftermarket gauge that was in there. I got it installed snugly and properly connected, but now when my truck is running, I hear a rapid clicking coming from the rear of the engine. Also when I accelerate, the clicking speeds up too, as if it's something rattling/loose inside the engine. Sounds similar to a kitchen timer. Don't have a clue of what's causing it.

Here's a close up video of the sound:
http://s1224.photobucket.com/user/gigabyteidna/media/IMG_04041_zps2dd03060.mp4.html