Rattle on first startup

Have been installing a JDM (50K mile) 3.4L engine in my '98 Tacoma 4X4 for past month. Started it for the first time this afternoon and it seemed to run smooth, but has a 'rattle' - more like a rat-atat. this sound reminds me of the sound an engine with hydraulic lifters makes before the lifters pump up. But of course the 3.4 doesn't have hydraulics. This is my first 3.4 install but not first engine swap. I have actually done maybe 8-10 engines altogether, about half of those JDM.
Wondering (and dreading) what this might be. I triple checked the cam timing when I put the new timing belt on, but could this be one of the cams off a tooth? Would it make that sort of noise? I will likely go out later and pull the cover off and check again. Right now just kind of bummed (and hot - 103 here today).
Thanks for opinions.

 

Auto trans? flex plate cracked maybe

 

Old cat falling apart from the inside. My old flowmaster cat failed after a year and made all sorts of small pings and rattles. If it's not welded together you can unbolt and check to narrow things down.

 

The 6cyl valves tend to get tighter/quieter with age. Cam timing off should not make a noise, just loss of performance. There's a bunch of 3.4's out there running a tooth off that don't even know it. "Piston slap" is not uncommon but usually rears it's ugly head in very cold weather start ups. It is very subtle and goes away in 10-20 seconds.

Crank pulley bolt tight, 217 ft lbs? Fan clutch bolts tight? Corn dog stick under the timing cover?

 

It is an auto trans, but I would have noticed a cracked flexplate. Also, new catalytic converter about 2 years ago. Noise is definitely coming from engine, tho, not anything below or behind it.
As for crank pulley, it's as tight as I can get it. I don't have anything that measures close to 217ft-lb. Fan clutch bolts are tight. In fact, everything is tight according to torque specs. I just pulled cam front cover off and found cams are EXACTLY dead-on lined up with their notches . . . when mark on crank is about 3/8 inch PAST the '0' mark. Which indicates to me both cams are a tooth 'behind' where they should be. I hear what Dirty Pool is saying, but could this possibly be source of rattling? Trying to figure out in my head whether this would cause some sort of pinging condition.

 

Video would help

 

Am currently in process of resetting timing belt and addressing a few other minor things. All this in between work and honey-do's of course. If I get the same rattle when I restart, I will try to take a vid and post it here. Obviously, it''s something not-right so I haven't run the engine more than about 30 seconds, just in case.

 

Trying to load a vid here, but not sure it's going to work. I took the front covers off to make 110% sure timing was correct, belt was tensioned, no play or worn bearings in anything - all checked out. Put it all back together and started and it ratattated again. Shot a short video and as I was doing it, the noise got quieter, the engine stumbled once . . . then ran smooth with no chatter! I let it run 20 mins, shut down, let it cool, started it up again and the chatter is gone. Woo-hoo!
I am hoping I didn't spin a bearing or ruin anything, and that maybe it was just part of the valve train running a bit dry till the oil got there - ??? I guess we'll see. If I can get this video to work, I'd still like your guys' opinion on what this noise might be.
As mentioned, this is a JDM motor install - one of those engines that supposedly has only 50K miles on it. It cost me $1,100 and did come with a one-year warrantee, so at least I have that to fall back on if something does crop up. But man, it was a bee-atch installing this thing. Never seen so many electrical plug-ins. Main harness has 60 wires bundled in there.
Well, I can't get it to load here, but here it is on YouTube: https://www.youtube.com/watch?v=UlzDgqc6T2g&feature=youtu.be

 

That sounds ugly. Like no oil pressure. Or. Jesus that's ugly. I dont even know where to start.

 

I agree. But since it smoothed out, no more noise. Runs perfect. Just took it on first half-hour drive (and to wash the truck) and it ran smooth with plenty of power, temp gauge right in middle. No leaks, no probs. Will probably take it on a longer trip before I put skid pans back in place. But keeping my fingers crossed!

 

Valve stuck/sticking open a tad from sitting under less than optimum conditions, then unstuck? Fits the sound and symptom.
I am assuming the "30 seconds" of the initial start up did not include any kind of driving or load that would have made the accompanying miss from a stuck valve more apparent.
Anyhow, keeping my fingers crossed for you also.

 

Or fuel knock as the air cleared out of the fuel rail?

 

Sorry to drag this back out. When I start my truck after it calms down maybe 30-45 seconds after starting - I notice a rattlish sound coming from the catalytic converters. It’s a 2011. Do they need to be replaced?

 

My 2011 has a slight rattle at start to sounds like it’s in the exhaust - happens like 1x a month. It’s always at start up when it happens. Only last like 1-2 seconds. Almost sounds like the Honda Accord VTC rattle that my wife’s car had. But that was like a 3-5 second rattle. Any ideas?? It’s so random and very seldom that it’s impossible to know when it will happen or get audio. One thing I did a few month ago was change the spark plugs to platinum plugs. Noticed a real rich smell and a lot of exhaust condensation after and still. Any relation?

 

Correction - I used Denso iridium plugs

 

That's definitely a valve train sound !!!

 

yep top end sound... sticky lifter bucket. If not to full on oil put a quart of marvel mystery oil in her... is isnt called marvel mystery oil for no reason, it does work.

 

Is this in reply to my post or the OP?

 

How many miles on the truck? And what engine/tranny? Also, when it does do the rattle, is it always when the engine is cold? Or will it also do it when hot? I would say if the truck runs good and you get no engine codes (have you checked that?), I wouldn't worry about it until it gets more pronounced, at which point I'm guessing it will be easier to find. It certainly could be the cat, but my V6 Taco currently has 305K miles, still has the original cat, and still passes CA smog with no problem. I have had similar clanky rattles on other vehicles turn out to be loose bolts or rusty/cracked heat shrouds, skid plates or other 'floppy' parts.

 

Yup, ugly sound for sure, I agree too, valve issues or oil pump lack of pressure