A common cause of flex plate noise are loose flex plate mounting bolts. If they are loose the flex plate will clank around as you step on & off the gas. Pull the inpection cover and see if you can move the flex plate by hand, without causing the crankshaft to move also.

 

i found a website where some guy was asking this problem also said it only happend when it was in gear and slowly would fade faster you go. he said he replaced the tranny and it fixed the noise

a few months ago maybe like 6 the transmission filter was clogged i guess and they replaced the filter and flushed it and put new fluid in it, i been reading some threads on here saying changing it can fail the tranny, can that be what this is?

 

hey there!

not sure if you got it figured out yet as you posted this in Feb.08 and its now a month later.
I had a similar problem with my 79 Trans-am. Yes i realize that this is a Camaro board but what the heck? Camaro/trans-am pretty much the same damn thing!

anyways..........

im willing to bet you the rattling noise you describe is a result of a faulty Torque converter. That rattling you hear most likely are the worn out bearinngs rolling arounnd inthe converter. Being that the converter is attached to the flexplate its a common assumption that the flexplate may be at fault.

Again.........im only suggesting this as a place to look, because the rattle and behaviour that you described sounds exactly what i went through. I too went through several trouble shooting methods before realizng my converter was toast. At first i thought it may be a worn U-joint, then a bad flexplate etc......

after jacking the car up securlywe could hear Ratlling and pin pointed the sound to the converter. Again with the car SECURE ON STANDS we put it in Drive andas the converter was spinning you could almost hear the rattling in sync with the rotation of the converter. The baffling part, as you described, was "why didn't it do it inneutral? all the time in drive and sometimes in reverse?"

i managed to pick up a brand new B&M converter with a 3200 stall for 125 skins on-line. fairly simple process replacing the converter, just a bit time consuming. Mind you, its probably alot easier replacing a converter on a 79 Bird then a 99 camaro.

I wish you luck! I'll check back and see if you solved your problem

 

While you were looking at the flex plate, did you check the bolts holding the plate to the crankshaft for proper torque? These bolts can loosen with time allowing the plate to move and make a clanking noise under acceleration & deceleration. The threads of thesebolts need to be coated with red Locktite.