engine noise on 1995 BMW 318is

my car having very noisy sound inside the engine what is the primary cause to this problem

Asked by for the 1995 BMW 318is
You need to see a BMW specialist. It could be a failing alternator or water pump, or a bad belt or worse, but have given me no good information in your question. A person would have to see the car and hear the noise to be sure.
Here's a directory link for you, but I don't know if it covers PR so you may have to find a guy on your own.