rattling/ loud vibration on startup

Does it sound like a upper engine noise like lifters/valves or like timing chain ect.? Have someone crank it up with hood up and you stand over it listen for the spot or area you hear it from, it may be something simple.

It sounds like it coming from under the engine. The rattling almost sounds as if its the exhaust rattling but its not the exhaust it almost sounds like it coming from under the oil pan?

Under or in the oil pan, toward the front or back of it?

I am not sure if it is in or under the oil pan. The sound is just coming from that general area.

Heat shield above catalytic converter? (Between converter and body metal). Or bolted around converter. I have to replace bolts and nuts on these all the time. Most have 4..one on each corner of shield.

Did they fill the oil and to the correct amount and weight?

That I am not sure. I took it to the same place as I always do and have never had anything like this happen. Again I am not saying it is due to the oil change but I just started hearing the rattling on startup a little after the oil change so I am guessing.

It Think the best option is to get it on a rack/lift and or jacked up and wait until its cool and start it up and see/hear it. If its in the pan then this is not good but may not be terminal so do put it up for yet with bad motor in listing. may just be a pulley, timing chain worn or oil pump or bad main bearing on the crank shaft or loose piston rod cap but only way to find out is to figure out where its coming from, if its in the pan, pull the oil pan and inspect the contents. AKA loose piston rod cap bolts ect, just replace with new bolts/thread lock and may just have dodged a bullet.

If that is the case then they will want to rebuild the engine just to cover their Axxxxes.

Oil pump Strainer may be clogged or partly or even dislodged a bit or loose if its internal there just is not much you can do but open it up and see whats going on, but if its heat shield or rust in the exhaust or a bad pulley or belt tensioner, worn timing chain parts (guides ect) then no big deal.

Make sure the dipstick is in and seated correctly.

I would definitely check oil level before You start your truck. I have family that have experienced the 0 oil change experience and paid for it. One left it empty and the other did not change anything. Oil or filter.

Just letting you know, I had my truck checked out and all it happened to be was a hole in the top of my exhaust. Every time I cold started my truck the shield above my exhaust would rattle against the exhaust until it got warm enough and expanded. I appreciate the help. This is a great cite. Thanks again.

Great.

#1 always check your own oil even after you had it serviced. I only trust two things in this world myself and my dog and often I trust my dog more than myself. Start with the easy stuff first, loose exhaust, brake, fuel, cooler lines that maybe vibrating against frame,engine, trans, etc. Check heat shields. If you still can't find it, check for the noise around your starter. You may have a cracked flexplate (flywheel). It'll sound like metal on metal vibration, or a quick tapping sound, or sometimes a mild grind that's not consistent. Often a cracked flex plate can be heard at start up and idling while in gear. Very seldom will you here it when the vehicle is in park or neutral.

Loud rumbling noise Underneath Truck when I'm driving The noise comes and goes 1994 Chevrolet Silverado

I have the same rattle on my 2018 GMC 1500 Sierra. Its about 3 seconds on a cold start. It is definitely coming from the exhaust. It almost sounds like a loose hanger or something. The dealer told me that it is the Exhaust Cold Start Buffer... I've never heard of that and I can't seem to find it on Rock Auto, etc. The dealer said it would be 1k to fix it, but that it was backordered with no ETA.