Prius 2 UK engine noise

Check your serpentine belt, sometimes when they are in need of replacement they make a cracking noise.

 

Very odd noise it’s out of sync with the rev of the motor like it’s just something loose in the motor clanking around
If it was me I would check the oil level and the coolant level.
Don’t bother checking the white overflow tank for coolant level take off the black plastic cover that’s covering the rad by taking out the 6 screws and open the radiator cap. Coolant should be at the top of the cap.
If low you have a leak and then

Get a flash light and look closely in the front of the engine check is the belt there like hc said and then look very closely for dried red specis that’s leaking coolant from a blown engine water pump.

 

My guess would be the water pump also but isn't there a tensioner for the water pump could be the bearing is failing. It only has one belt so I would remove it and start it up and see if the noise goes away. Only do this for a short period of time.

 

Water pump and/or belt tensioner is my vote. This is easily verified.

 

yes thats a good suggestion but the noise is out of sync with the engine revs to me but who knows. The belt trick is easy and takes the pump and tensioner off the table.

Hope the OP never ran it so low on engine oil it threw a red triangle of death cause that will make alot of noises lol.....

 

Once all external noises are eliminated like the water pump and tensioner the noise has to be internal if I din't miss something.

 

Weeping water pump means it’s blown.

Checking the oil every now and then leading up to no oil on the dipstick means the engine is damaged.

Higher dimple on dipstick means that’s the full line and that’s where the oil should be at all times.

 

Geez. Just replace the pump and be done. Do you want a cheap part to be the cause of leaving you stranded some time in the future? The water pump is telling you to replace me soon w/ the dried coolant on the outside! You clearly like to push your luck, two years later, with the audible clue telling you to replace me yesterday. This assumes you diagnosis is correct: engine not on, sound disapears.

Loosen the belt and spin the water pump and belt tensioner bearing by hand. One or both will likely be binding and you will feel it. All three of these parts (pump, tensioner, belt) are cheap, esp since they last so long; cost per mile will be bery low.