Waterfall behind dash

[87supraturbo]

I've read all the threads about the BHG symptoms and my car has none of them accept the waterfall noise when i start it up, i just got it back from the mechanic yesterday and got him to check for a BHG and he said it was fine, also all the fluids and stuff were replaced and there was no coolant in oil, oil in coolant and theres no white smoke from the exhaust. So my question is is there anything else that might cause the waterfall noise or is that a direct sign of a BHG??

Thanks,

Matt