rod bearing noise....again?!

[davidpertuz at mindspring.com]

I just hopped into cold my G20 to carry some sound equipment down the street for my neighbors, and as I go through the 2500-3000 rpm range, I hear....rod bearing noise?!?

That is what I assume it to be anyway. My SE-R developed it a couple of years ago after 220k or so and I still haven't gotten around to replacing the bearings (granted, I didn't drive the car for almost a year until the other day) but I am surprised and worried to hear the same sound on my G20. 

I had to put a new engine in the G20 not too long after I got it, and about 30,000 miles ago I got an engine from Soko in Chicago (I did the swap in Chicago, so I went to the warehouse and picked it out myself) and swapped it in. While I was doing this I put new rod bearings in it since it's cheap, super-easy on an engine stand, and good due diligence with an unknown engine. The engine was sparkly-clean inside, and the bearings I took out looked A-OK.

This leads me to think of two questions:

1)If this is rod bearing noise, what could I have done wrong that my fresh engine seems to be developing it?

2)If this isn't rod bearing noise, what else, if anything, could it be that sounds similar? 

I'd never heard it before I heard it on the SE-R, but right away that's what I thought of when I first heard it. It's sort of a sewing-machine sound that comes in arouns 2500-200 rpm when the engine is cold.

Thoughts welcome. It's gonna suck (and be discouraging) if I have to do this on both cars.

thanks,
David