2000 chevy impala rattling or knocking noise when turning over is quite loud and does it a little when shut off. maybe a main bearing.car is beautiful and just ticked over 100k never driven over 50mph thats the speed limit in my state.help please.oh yea has 3.4l.

Inside engine ? rod bearings or main bearings .

Bad knock sensor or rod bearing/main bearing failure.

you have a bearing defective !!
it need to be replaced to avoid damage other parts $$$

Could be a tire hitting the inner fender skirting. Check both front tires to see if they are clean/scraped right at the tread and side. This is a good indication that the tire is rubbing something. Also, since your turning right, you put more weight of the vehicle on the left side. You might want to check the front and rear wheel bearings on the left. I've heard them click before, but only under pressure.

Knocks ---big ends or main bearings
rattles-----tappets worn or loose or hydraulics leaking down too fast
Tinny noise ----water pump bearing , fan hub.
Sharp release of air noise --- broken exhaust pipe
for starters
Take your pick

You need a trained technician to listen to this, but it sounds like a connecting rod and or a crankshaft main bearing noise. I lean more towards the rod knock form a worn out bearing.

might be the valves have been damaged running without oil
- or the crankshaft / camshaft / main bearings
most probably you have to let the engine be rebuilt by a mechanic
(expect cost of more than US$ 2.000)
or get another (used) engine at a scrapyard

can be anything if noise while driving cv joint-hub [wheel bearings] exhaust hanger broke -transmission- brakes-if while idling[engine knock] rod-pistion

engine big end or main bearing.

Hi shwangod, you said it was a "heavy knock" and it began climbing a hill, could you give me a little more info, mileage, overall condition,2 or 4x4 am assuming this is a small block 350 cid, obviously there are different "knocks" for different problems, lifters do not knock they will click or rattle and are easy to adjust, a timing knock is the resultant effect of incorrect timing usually on the low side and is also easy to determine.A wrist pin knock associated with the piston boss pin can sound like a main bearing knock and is worse when the engine is cold and will subside as the engine warms up, the main bearing knock is the heavy knocking that doesnt quit and can lower oil pressure (operating) you can plastguage the mains to determine the amount of wear and if you are lucky you can roll in a set of bearings, when you drain the oil look for metallics, specifically brass, personally I am not a fan of upper or lower engine rebuilds but prefer to "Rebuild" the entire engine. I hope this helps you,good and let me know how you make out.