My son's 95 isuzu rodeo has developed an engine noise. It is a loud clatter. Called a mechanic he suggested changinging oil and replacing with a synthetic. Tried that, didn't help. Took it in, he thought it might be a cracked flywheel, that checked out negative. Doesn't think it is internal engine D/T the fact that it is very loud at idle and decreases and stops with acceleration. Any hints or thoughts would be greatly apprecited, my mechanic is stumped.