Hello all, this enigma of a car has sprung up another issue for me. For background, it's a 1987. This is a newly rebuilt NA engine with new bearings that has about 570 miles. I recently changed the oil to 10W40 as it's quite cold and that was what people recommended for the winter. Also, in that video my trailing coil is dead, not sure if it helps but that's that. Either way, it was about -5 fahrenheit or -20 Celsius, and after somehow getting that engine started, above idle it would make this buzzing/vibration noise that was loud and concerning and got faster/louder with rpm.

This might need a stethoscope to figure out exactly where it's coming from, but I think it's coming from the exhaust side somewhere, maybe towards the bottom. But at idle there's also a repeating ticking sound from the flywheel area possibly - I took off the inspection cover but didn't see anything out of the ordinary. As you can see, I'm also running it without the belt there to eliminate one more possibility or where the noise comes from. Then after about 2 minutes of it running like this, it slowly subsided.

I gently drove it for about another minute and it was gone. Definitely something temperature related. I don't know if it's just still unhappy with 10W40 in these temps or something is vibrating against something else. Frankly this makes me not want to run this car in these temps at all and I'll probably stick to that. Know, however, that I immediately had oil pressure when starting, so I doubt it is an oiling thing. Also clutch in vs clutch out made no difference to this sound. Anyways, I wanted to see if you guys had any input as it was pretty concerning. I appreciate the help!