Tinny rotational rattle on start up

I am new here, looking for some advice!
My recently purchased 2007 Tundra 5.7 (238k) has a loud tinny rattle on start up, but not every time. Rattles for maybe 2-3 minutes. It think it is one of the belt driven components, and sounds like a small tin can rattling around the fan? I have changed the tensioner assembly and the idler pulley so far, because they probably were due. Could the fan clutch? or AC compressor be the culprit? BTW, the ac did work after charging, but has a bad leak. Thoughts on likely leak location would be great too.
I don't think this rattle is timing related, it doesn't sound deep enough.I have checked heat shields too as the sound is similar.
Thanks for any help or advice!
Steve.

 

Check the catalytic converters. I had a rattling sound and thought the worst and it turned out to be the honey comb inside the catalytic converters. When the exhaust is cold tap on each one . Does it increase when you press on the pedal more ?

 

Thank you for the reply, that is something I hadn't heard about. My noise sounds like it is more in the front, but maybe not. I will check about the rpm/ noise ratio. I just bought a cheep stethoscope, might try that at the cats.

 

If the cats are clogged, it would make like a thumping sound if you hit it with a rubber mallet. Post pics of the cats...they may be the original ones. Does the exhaust smell at all...like rotten eggs? Also, check the heat shields around the exhaust. They will rattle if they are bent or loose.

 

It is raining every day here in NH, I will have a look and at the cats this coming weekend. Thankfully I don't smell a rotten egg smell, I had a car that smelled like that once. Disgusting smell. I am hopeful that there is a loose piece in my drivers side cat, as was suggested to me. May have to redline that motor to seat whatever came loose.
Thanks and will get back with a result!

 

What weight oil are you running? Check the timing chain system.

 

I just fixed this same problem yesterday. I had 2 bolts fall out that fasten the heat shield around the cat under the drivers side. Easy fix. Was annoying to figure out and took me a while to find.

 

@Urbandalefirefighter

Could u describe the location of those bolts a bit more, I feel like i have this same problem. I wanna fix it bc it irks me hearing the small rattle. I just replaced the flanges bc of exhaust leaks, and the sound has stayed before and after that. Thanks man

 

@RockWarriorLover

Sure. Here’s some photos. Mine is right behind the drivers side wheel. Heat shield bolts. Check all your cats, not just this one.

 

Thanks so much man, i knocked on the rear driver one and its making the sound, will try to tackle it later sometime today.

 

My bet is the heat shield as well. Happened on my 07 4runner and about drove me nuts......simple fix as @RockWarriorLover suggested.

 

Fixed it after looking under and further inspection, I saw I was missing a bolt and the clamp was just sitting and causing the chirping. Thanks for the guidance, I just found a good bolt and matching washer and nut to put on it, make sure its stainless steel so it doesnt rust.

 

To Tundra1D6!
My noise is a different than chain slap etc., although that will probably be be coming! Thanks. My noise is tinny and I think rotational. Can't look till the weekend, and then it doesn't do it every time!! Appreciate all input! Stay tuned

 

I just replaced my belt tensioner 3 weeks ago, and it started making noise right around 175k miles. Also a good time to change the belt. It was a small chirpy sound, not sure if its ur problem, but i just wanted to help

 

So.... it turns out the terrible rattle on start up was caused by the Mobil 1 oil, in the factory recommended type. The truck sounded fine when I got it, after a jiffy lube change, (according to receipt found). I changed oil and filter right away, for piece of mind, and the sound started soon after. Now, I bought some super tech synthetic 5w-30 just to see, and have no more noise at all. I have seen this complaint on the 5.7 engine a few times now, for me it seems true. The Mobil 1 did run out like freakin water when I drained it after 1200 miles.
My 2000 tundra, with the 4.7 loved it's mobile one, it has 320k miles now!