I have a mysterious "rattle" noise coming from my 302. The noise is only heard at idle (750RPM) and goes away if the engine is revved up. It sounds like it is coming from around the crankshaft pulley area. It's not loose and doesn't appear to be damaged. The engine and transmission were both rebuilt about 3000 miles ago. The cam, lifters, and timing chain were replaced at that time with a Comp Cams 31-255-5 with matching components.

I spent 4 hours checking over my whole engine. It doesn't sound like the top end. I have eliminated the following:

- belts and pulleys are fine
- water pump is good
- power steering pump is good
- alternator is good
- fan is good
- motor mounts are good
- torque converter bolts are all tight (I discovered my dust shield was missing)
- flex plate is good
- starter bolts are tight
- crank bolt is tight
- I tried turning the crank pulley, but it was too tight to turn by hand

With the engine running, I got under my truck and got a good listen, and the noise seems to be concentrated in the oil pan or where the transmission bolts to the engine. The odd thing is, when the engine has cooled off a bit and I start it again, the noise is greatly reduced. As the engine warms up, the noise gets louder and more irritating. Again, the noise is heard at idle and goes away when I give it gas. I dropped the transmission a few days ago, and the flex plate is in almost perfect condition.

It sounds like a hollow rattle, almost like a loose bolt or baffle. What in the world could that be? I've checked every nut and bolt in the area, but could not find anything loose.

 

Exhaust leaks can sometimes mimic rattles.

 

I had a bad torque converter on my F250 that sounded similar to that, but it did it much more at higher rpms.
If it's a rear sump engine, it may be that the oil pump pickup isn't bolted tight to the main cap, and is vibrating.
If you have a mechanical fuel pump, a loose eccentric is also a possibility, or a weak fuel pump spring.