Motor making very loud noise

try finding the loud motor try to add oil to it if if doesnt help replace fan motor

Replace oil and oil filter the oil is clogged up and needs to be replaced, Replace oil with a High viscosity oil you require more lubrication when cold a good Motor spares will be able to assist you with the correct oil,The noise it makes is cause the oil is not lubricating the cranck shaft and bearings and hydraulic tappets this is like a rumble noise,Only happens when the motor is not getting a good lubrication Caution if this continues to happen the motor will start to run dry and seize all bearings starting with the cranck shaft bearings.try to get synt synthetic oil expensive but will work .But do ask where you are buying for the best oil for low temp weather they will assist.

Maybe the cpu fan is fubar - check that out.

I would hope you checked the oil level & for leaks
also,before coming here

Hopefully you haven't ruined the motor already,that noise
is the sign of possible serious damage

To narrow it down, while the engine is running, don't get near moving parts, you can use a long piece of steel, metal, put 1 end on the valve cover, the other to your ear and listen for rattling. You can move it around to narrow down the source of the noise. It's like a stethoscope but works well. I use a 3' long screwdriver.

you could have sludge in the crankcase that is blocking the intake screen for the oil pump ... that happens a lot if oil isnt changed regularly .. in some cars it happens even if you do. ...the clatter you hear is the valve lifters collapsing . they need oil pressure to keep them extended properly ... if your oil pump isnt bad it soon will be .. it needs lub also or it will quickly be damaged ...sometimes you can wash out the sludge with kero/oil mix but the safe thing to do is drop the pan .. clean up the sludge and replace the oil pump.while you are there ...once you have the pump working you can first run cheap oil to clean out things ..then drain and install synthetic ...that will do a better job of cleaning out remaining sludge ... of course make sure you have the proper amount of oil to start with .. make sure there is no water in the oil (milky oil) .. make sure oil filter is not clogged ...some oil filters have a one way valve ... that can stick if the car isnt run for a long time .. ....

Put some lubricant, oil, WD40, etc. on shaft of fan. Spin the fan with your finger and work the oil into the shaft until the fan spins freely again. Reassemble and problem will be gone for 2-3 weeks. Repeat again until you want to replace the fan motor.

no it's can be repaierd but it's overhaul time.

A screeching or squealing noise usually comes from the fan motor. There may be an oil port and you can buy a small telescoping oil bottle at a super hardware store or an a/c supply house. Before putting in he oil, remember to TURN OFF THE POWER TO THE UNIT and only use a light squeeze on the bottle - over oiling will cause a mess inside the motor. It may be a sealed motor and no oil ports. In either case, budget for a new motor as if it's to the squealing stage, the bearings are already damaged and it's a just matter of time before before the motor bearings fail. If possible, get oil on the bearings ASAP - and use the proper lightweight oil for made for this application.