Crank or HB chatter
 

305TBI. Chatter comming from front of crank by Harmonic Balancer. Only after its warmed up, always around idle or under 1300, at a stop in drive it sometimes sounds very nasty but pop it in N and it quiets down alot. Took off the belt and it's deff not any other accessory. In park it could be very quiet then all of a sudden it starts a loud chatter, I give it a little gas and it goes away, let off gas as it falls back down to idle chhxchchx.... ?????

mines been doiin that since i bought it 5 years ago....

I know you said by the front of the crank but maybe the torque converter things can echo in the engine bay and throw sounds off.

Yeah Mine has been doing it for about 4 years. I know its not coming from the torque converter cause i used a stethoscope on it and it sounded like it should. Im thinking the timing chain hitting the cover. But why only after it's fully warmed up??

Could be a lot of things. Maybe a lifter? Does the sound change with RPM?

mine only does it at idle some times, goes away with any higher rpm

the sound is always the same rattle/chatter, it just gets louder, quieter, disappears then comes back at the next red light. same as maroman88

ehh i only get it in park and neutral, stopped at red lights with it in drive it doesnt do it.

actually my car wont stay running while in pork or neutral right now lol so i have a bigger problem

its the timing chain flopping around in the cover the smallest or hits will make all kinds of noise at slow engines speeds -- and it will do it for years 10,s of thousands of miles -- just what we have seen i the shop -- jz

thats exactly what i thought but never had anyone look into it, if it aint broke im not guna fix it :)

It soon will break with the way it sounds, also if it has enough play to flop around and the noise gets worse, then it quite possibly could slip off

for many years GM used a plastic top gear -- for sound i guess and the teeth would come completely off the gear - just before it happened the car when hot would be real had too crank over like the dist was way to far advanced if you know what i mean by that -- today the gears are steel and the chain is a double row type so it is very durable and even when stretched out it still works - but some day it will catch the next tooth behind the chain and it will stop usually at idle or real high RPMs -- jz

Yeah, the cam gears had nylon teeth that would wear and break off. Not what you want when dealing with your timing.