New fun rattle!

[KSSVO]

Let's try and diagnose. This rattle shows up around 2500ish rpm. It increases with rpm from there, but there is no discernable change in the way the car runs. No stumble, no stutter, no shakes. Just butter smooth (for a Lima...). In an attempt to see if it would break in the driveway, it proceeded to lay down about 125 feet of stripes with no issues hitting 6000rpm.

There is a maybe a small noise at start up, but this car has always had a noisy T5 on start up. There is no noise at all at idle. No glitter in the oil. Great oil pressure. I have the cam cover off and all followers are on their lobes and HLAs. They all have similar feeling preload from the HLA. My initial thought was a weak HLA losing its ability to keep up around 2500+rpm. The engine appears to be the original at almost 100k. So it likely needs valve springs anyway.

I'm at a bit of a loss. I was thinking I'd find a rounding cam lobe or soft HLA with the cover off.

https://youtube.com/shorts/6435u34gghE?si=YLfbHgSv-_JaYXSj

https://youtube.com/shorts/5XvDOOHgf48?si=DC5GweSnVErUmM1R

The sound is more prominent under the car, but I think this has more to do with the sound being more isolated. Could it be clutch related? The cable/quadrant all feel fine. The clutch clearly holds better than the tires do. But the TO bearing could be bad and chattery. But it makes the sound in gear and out of gear though.

[GAboySVO]

Here is my guess: It sounds like one of those spring steel heater hard line clips is loose and making the buzzing noise you are hearing. Try wedging a rag between the two hard lines and see if the buzz goes away.

[86SVOwner]

It might be the catalytic converter. Mine rattles like crazy because the guts have all broken apart.

[gbeaird]

It might be the catalytic converter. Mine rattles like crazy because the guts have all broken apart.

Our 3rd Gen Camaro does that. It gets quieter once warmed up, but has a distinct rattle when first started.