https://drive.google.com/file/d/1iQsurVJiD2RyzFy-Vbm1PJ5mbtepFu0E/view?usp=drivesdk

My 1985 Firebird, LG4 305, started to make metallic rattle sound when under load. It seems to only be around 40-60 mph and intermittent at that speed. Doesn't make the sound at lower speeds or idle. When I give it throttle the rattle starts, and when i release it goes away. I have secured ans tightened everything I can find under the car and am at a loss. Its driving great, shifting great, and has no codes being thrown.

I attached a link with a video. A bit hard to hear, but i make the sound occur 3 times and coast in between the sounds. Any suggestions would be great!

 

Probably spark knock.

A combination of too much ignition timing advance, and too low-quality gasoline.

Put some premium in it. See if it changes.

 

Yup. Sounds like pinging. Maybe bad gas if it was fine before.

 

Thanks for tips. Oddly enough....again, it seems as though it was my speedometer cable. I lubed it last week when it was making a ticking sound. Low and behold, as I was driving it today i noticed the needle bounce and the sound become.more prevalent.

so, i took it off today ....trying to back track...and boom, no more sound. Oddly enough, its a completely different sound than it was before. I ordered a new one piece cable to see if that will resolve it.

if it doesnt, i will look into the timing as suggested.

 

If the sound turns out to be spark knock, I'd recommend looking into the gas you're using instead, and leave the timing alone.

Since speedo cables don't really care about "under load" and "accelerating" and all that (although the speedo gears sometimes do), you may find the noise returning. More accurately, ONE of the noises returning... you may have had TWO going on at the same time. The "completely different" one having been the speedo cable, the other being spark knock aka pinging.