Rattling noise under hood near firewall

[mdb20]

I've got a puzzling noise that seems to be coming from the engine compartment on the drivers side possibly near the firewall. I just started noticing this sound about a month ago and it's been intermittent, so it hasn't been a big issue, just annoying. At first, I thought that the noise was A/C related, as I've been using the A/C pretty frequently since its summer and its been hot. Lately, the noise has become more frequent and happens when the A/C is not in use as well as when it is in use. The sound resembles ruffling a bag of leaves around or a metallic kind of ruffling around. It gets louder or more pronounced when the RPM's rise. That's the best I can describe it. It happens while driving straight, under load, not braking or turning. I notice it more when the RPM's are higher and the car is under more load and/or more than light throttle. 1/2 throttle or more. One of my Tech's at work first thought that it may be a bearing in a pulley or something, since the pulleys are on that side of the vehicle. After putting the vehicle on the lift at work today, now we're inconclusive on our thoughts. We were able to duplicate the noise with the vehicle under load while off the ground on the lift, but not able to diagnose where or what it's coming from. The tech thought today that it could even be an exhaust leak or something. Unfortunately, it's tough to describe the sound and it doesn't happen all the time when driving. **Any thoughts, ideas or similarly confusing noises?

Registered and logged-in users don't see this ad! Register your free account today.

[Line7]

Heat shield or catalyctic

[AcuraLsSE]

If it were an exhaust leak I would think you would hear it all the time. Might want to pull off one of your timing belt covers and check in there, Just a thought. Most of the time a cracked heat shield would be sensitive to a specific rpm. Hard to tell when I don't have the car.

[pslsnakes]

Sounds me to like a heat shield

[mdb20]

I checked the heat shield on both the OE header and the Cat. Neither was loose or causing a rattle, but I still hear the noise. Last night, I tried to get a sound clip of the noise while driving the car, but all you could hear was wind, intake noise and distortion. At this point, I'm thinking that it's not the cat or header heat shields and that it may be some kind of an exhaust or vacuum leak of some sort, or something internal engine perhaps. It's tough to diagnose, since the car has to be moving down the road to really hear it and you can't use a stethoscope to listen to specific areas under the hood unless its parked. I'm gonna check on Mitchell for TSB's for the Teg and see if there were any for these symptoms. Ideas?

[cruzalekz]

its your bumper

[AcuraLsSE]

Originally Posted by mdb20

I checked the heat shield on both the OE header and the Cat. Neither was loose or causing a rattle, but I still hear the noise. Last night, I tried to get a sound clip of the noise while driving the car, but all you could hear was wind, intake noise and distortion. At this point, I'm thinking that it's not the cat or header heat shields and that it may be some kind of an exhaust or vacuum leak of some sort, or something internal engine perhaps. It's tough to diagnose, since the car has to be moving down the road to really hear it and you can't use a stethoscope to listen to specific areas under the hood unless its parked. I'm gonna check on Mitchell for TSB's for the Teg and see if there were any for these symptoms. Ideas?

If it only can be heard while driving it sounds more like a tire/suspension issue

[mdb20]

I'm really doubting that it's a tire/suspension or bumper issue at this point since the car still made the sound while we had it running on the lift off the ground. I checked for TSB's on Mitchell and all I could find was stuff about the heat shield that doesn't seem to be loose.

[AcuraLsSE]

Originally Posted by mdb20

I'm really doubting that it's a tire/suspension or bumper issue at this point since the car still made the sound while we had it running on the lift off the ground. I checked for TSB's on Mitchell and all I could find was stuff about the heat shield that doesn't seem to be loose.

I forgot that you had said that. I'm still thinking drive line related issue if you can't hear it unless the wheels are spinning.

[Lynxs1981]

I would check the mounts. Sometimes when the rear mount wears, it makes odd noises.

[Line7]

Ive never experienced any sort of sound you are describing that ended up being a transmission/suspension/engine problem. Although its tough to describe a noise in writing, and if you are positive its not your heatshield or the cat, then it might just be an exhaust leak. Is it really loud, or do you just hear it when you are driving next to a wall or another car? Does it sound like marbles in a tin can?

An exhaust leak is really easy to pinpoint. Put in on a lift and you could actually see exhaust coming out of the leak, or put your hand next to it and feel it, or put a mirror to it and see if it fogs up. To diagnose a bad cat, just hit it with a wrench and you'll hear that the insides of the cat are broken and sounds like marbles in a tin can, same with heatshield.

You really need to put it on a lift and really check shit out under there. Good luck.

[mdb20]

When I drive it on the highway at higway speeds, its much more pronounced and louder when I downshift to 3rd gear. 4th gear is a little quieter and 5th gear its the most quiet but I can still hear it. It seems to get much louder when the rpm's rise and much more noticeable when I'm at 1/2 to full throttle as well. Not sure about the marbles in a can sound though. It's more of a metallic buzzing type of sound that seems like its coming from under the hood right in front of the firewall.

[joe_kewl81]

the only thing i can think of is the master cylinder is right there. A vacuum leak would certainly have a unique noise, there is a small plastic valve that goes to a hose on the intake for vac. maybe replace that valve?