Could be many, many reasons. Have a qualified mechanic listen to it, he should be able to diagnose the cause.
You cracked the block.
Unless it is storytime (and the book is about firetrucks), it usually isn't appropriate to make fire engine noises because doing so will be disruptive for others who are using the library.
Dogs make howling noises in cars.
In Subaru Car. Make clicking noises when work.
a mouse lives in the dashboard
Perhaps you have aground loop.. Make sure the amp and head unit are grounded to the same location.
It is probably a wheel bearing if it only does it while moving.
No, it should be quiet if assembled properly.
they make harsh hissing noises.
Gorillas Make Monkey Noises But With A Lower Voice. Gorillas Make Monkey Noises But With A Lower Voice.
you can make noises by tapping them together
Mine was doing the same, it was making very loud weird noises. It was a loose connection so maybe check your connections? worth a try