Crackling/grinding noise

[jojo-munson]

Hey all, recently my 72 c20 350 has been making an occasional crackling/grinding noise, and the Google can't find an answer. The noise lasts 1-2 seconds then stops. It's not consistent and I can't seem to reproduce it on command. Originally I noticed it while driving in first at idle, and thought it was coming from under the cab. But yesterday after replacing a cracked exhaust manifold and while letting the truck idle in park, it made the noise. Except this time it sounded almost like it was coming from the engine. I'm scratching my head trying to figure out what it could be.

Some things I've done already. Checked the power steering pulley and alternator for wiggle. The power steering fluid is also at the correct level. The u-joints look good too. I fixed a broken exhaust hanger so the pipes are pretty sturdy. I have an oil leak and super small transmission leak (Cherry red on the stick though which is great), but those have been there since I got the truck and this is a new noise.

Do y'all have an suggestions for things I should check? I know sounds are real hard to describe without actually hearing them, but I can't seem to catch it on video. Thanks in advance.