ok rebuilt 350 chev (local shop) ran fine when I put it in, did the cam break in and took it for a drive around the parking lot, still worked fine, week later take it out for flex testing and it sounds a bit noisy, no when I rev the motor up with no load I have what sounds like a bottom end noise, if I back the timing way off (like to the point it makes zip power) the noise sounds very quiet, almost like an input bearting rumble, push the timing up till it almost has trouble starting and the noise is very apparent, I can hear it in the cab driving around the lot, changed the distributor, pulled the front belts, no change. got underneath with the stethescope and listened to it, very loud at the front of the oilpan sump and in the middle of the passengers side valve cover but quiet everywhere else, no noise from the tranny case anywhere.
any other suggestions on what to check before I send it back?

Cam speed or crank speed? Heavy knock or light tap? You could try pulling plug wires to isolate a cylinder.
If it's got a warranty I'd make the shop worry about it, tho.

as far as I can tell its crank speed, light knock that seems to be fairly constant although it may get heavier with a load, little hard to hear over the boggers, I tried pulling the wires and it seemed to have zippo effect on the noise.

I would cut the oil filter in half and look for chunks. I wonder if a piston skirt collapsed? Does it burn oil, foul plugs or anything?

no oil smoke in the exaust, plugs indicate a bit rich but hard to tell cause I havn't driven it under load yet so I may just be seeing the choke. I don't think its piston cause it dosn't seem to be really load sensitive, I had the throttle wot in the parking lot spinning the boggers and the exaust covered any noise it made (my exaust is pretty quiet if it wasn't right behind my head I wouldn't be able to hear it).
what i really need is anything else to look for, all I have to do is be sure its engine, if it is the rebuilder pays for the install of a new engine, only thing is if it turns out to be somethhing I did or put on then I pay to fix it.