Engine rattle sounds like a diesel?

Hello,

Usually you will get a rattle when something comes loose or broken.
If you have a leak in the exhaust manifold it could make the engine sound much louder and will rattle.
The exhaust system in the car uses heat shields over the manifolds, catalytic converters, you could have a shield come loose and make the rattle.

As you say you can hear the rattle from the side of the belt, you could have a faulty harmonic balancer that crating the rattle. It is the crankshaft pulley.

You might find this video helpful:

https://youtu.be/OTeg2CUB5NE

https://www.2carpros.com/articles/rattle-noise

Please let me know of any questions.

Thank you.