Weird sound on light acceleration...

[ecrabb]

I'm probably going to have to try to get a recording of this because I can't imagine anybody knowing what the hell I'm talking about. But, I'll try anyway... On very light acceleration... Say one-third to one-half throttle... At around 2800-3200 RPM, I hear a little... Sound. It's kind of like a whistle, but not a constant or smooth whistle... It almost sounds a little like the Jetsons car sound. It's like a "rattle" but higher-pitched, or a "stream of bubbles" sound. I have thought an exhaust clamp or hanger or something similar, but it seems really high-pitched. I'm just coasting along, it doesn't make the sound. If I push the throttle to one-third or one-half, I hear the sound in the 2800-3200 RPM ballpark. If push the throttle much beyond one-half point, the sound either goes away, or is drowned out by the exhaust note.

Any ideas?

Thanks!

SC

[johnrando]

Stock exhaust?

[ecrabb]

Stock exhaust?

To be honest, I have no idea! I haven't been under the car to know. It does sound damn nice and throaty, but knowing who has owned the car for most of its life, and that there are no other obvious modifications that I can see, I'd imagine it's stock. But, I guess that doesn't really mean a thing.

I sold my jack and stands when I moved last year, so I'll have to put the rear tire on the curb so I can slide under in the gutter and check it out. It could certainly be a weird rattle - like a parking brake cable rattling on the exhaust only in that specific RPM range.

I have some investigatin' to do.

Actually, I need to find a ZHP owner in my area so I can meet up and do some comparisons!

SC

[Newjack]

Inspect upper and lower intake boots for rips or tears.

"Stream of bubbles" lmao

Sent from my Nexus 4 using Tapatalk

[ecrabb]

Inspect upper and lower intake boots for rips or tears.
Good points. We have company this weekend, so I won't get much done, but I do plan on at least getting under the hood and looking it over closely.


"Stream of bubbles" lmao
Figured somebody would enjoy that. It seriously reminds me of the Jetsons car sound, but just higher-pitched and quieter.

SC

[SoCalZman]

I have changed the DISA valve, intake boots, and changed intakes over to the BMW performance intake. I too have this light whistle. Been like that since I got the car. Never have been able to find the source. The car doesn't seem to care.

[ecrabb]

Fascinating. I wonder what it is. My biggest concern was that it was valves or something, but I'm about 95% sure it isn't that. I'm running decent gas (91), and it's only in mid-range RPM, not down load where you'd expect pre-detonation. It sounds like undercarriage and/or rear, and seems to be independent of gear, and at a specific RPM range, which makes me think it's exhaust-related.

I had guests all weekend, so I couldn't do anything with the car (other than drive it a little), but this weekend, I'm going to try sticking an audio recorder in a couple of different locations on the car and see if I can locate where the sound is originating, or at least get a good recording of it to share to see if it's the same thing you're hearing.

Cheers,
SC