Just guessing, but soft valve spring or stuck hydraulic lifter?

Well, the car suddenly lost a whole lot of power, and didn't want to accelerate at all. It wouldn't go over 2K RPM in drive. Car felt very heavy. The funny thing is, other than that sound, there was no other sound, car idles fine. I stopped the car, and checked the dip sticks (both trans and oil), and found no metal evidence at all.

I dropped it off at the local GM dealer for diagnostics. They are going to tell me what the problem is on Monday or Tuesday.

So what was the issue? Did you find out yet? I'm curious as to what it is/was...

Unfortunately, absolutely no one could tell me what it was, not even the tech at the GM dealer. The best he could do was guess. He said it was a main bearing.

Right now the car is in a shop, and I'm swapping an engine from my older 95 into it.

Sounds like a bearing or broken valve spring.

That'* one of the first things I looked for. There was no broken valve spring.

The sound was definitely lower end; it was not something that sounded like it was even near the valve covers, or in the middle of the engine.

Update:

Swapped engine from another car. The knocking sound is GONE. Finally!

But an original sound remains. Sounds like a bunch of marbles being rattled around around the driver side of the engine bay. It'* definitely the exhaust/transmission, but I can't determine where/how.

Any ideas?

Stuck lifter, bent push rod, broken valve train. I say pull the UIM and valve covers and give it a once over.

No, I swapped the ENTIRE ENGINE. Top, bottom, accessories, everything. This is an engine from a known good working car, so it'* not the engine at all.

The sound is from the trans or the exhaust, but I wouldn't know where to start in diagnosing.