98 328i engine thumping noise

my car starting making a thumping noise(sounds like a bad wheel bearing or something along that line) but I have found that it is coming from the engine area..BMW dealer says doesn't know what the noise is and can't repair it. (but they have had 2 other 328i's in the same years with the same noise and weren't able to fix it)
Please help!!!! I hate the noise! It makes the naoise all the time when accelerating!
What could it be?

ihope i dont find out man. i have the same car good luck,i'll ask around.

doesn't the wheel bearing make a whizzing noise?