Dear Tom and Ray:
My 1995 850 Volvo GLT sounds like there's a hurricane under the hood. This sound started as a barely noticeable hiss at high rpms but has gotten a lot worse. It sounds, quite literally, like a hurricane is whirling around under my car. It is quietest when the engine is cold; it's loudest once the engine is warm, and during acceleration. I can barely hear it until I step on the gas. It seems to be coming from directly behind and underneath the motor. Any ideas?
TOM: It would be interesting if they named hurricanes after things that sounded like them. You know, "Hurricane Transmission Rebuild."
RAY: The noise could be caused by any number of things, Devin. But we can help you narrow it down.
TOM: First, you need to determine if the noise requires the car to be moving, or will it occur when you're in neutral and just stepping on the gas?
RAY: If the gusts blow when the car is in park or neutral and sitting still, then you can rule out things like the transmission, the differential and the wheel bearings.
TOM: And if you can get it to make the noise by just revving it up, then diagnosing it should be a piece of cake. You get an assistant to step on the gas while you stick your head under the hood and figure out where the noise is coming from.
RAY: If it's hard to tell -- sometimes noises bounce off so many surfaces that it's hard to find their origin -- a piece of rubber tubing can sometimes help. You put one end in your ear, and move the other end around the engine, isolating different sections of the engine compartment, until you figure out where the noise is the loudest.
TOM: Then once you fix the car, you can drive to the emergency room and have the tubing removed from your ear.
RAY: If I had to take a wild guess, I'd start by looking at the snorkel between the air filter and the throttle. If that's partially disconnected or cracked, you'd hear air being sucked in through that breach instead of passing quietly through the air filter. That could be very loud.
TOM: But it could also be an idler pulley, a belt tensioner or a half-dozen other things. Once you narrow down the location, though, you'll be 90 percent of the way to fixing it -- the other 10 percent being money. Good luck.