tohlenforst

My car has had this issue for quite some time now (I just recently started to try and fix everything wrong with it since I could not before) but it has recently gotten louder. Whenever I decelerate or accelerate around 2-4k RPM there is a loud rattle/vibrating sound. It sounds like it is coming from behind me but I cannot be certain as there is a lot of cabin noise when driving. I'm going to be installing insulation soon to make the overall noise less noticeable, but I figured it would be best to fix as many noises as possible before making it hard to hear them. I recorded a video that you can kind of hear it in. Below are also timestamps of the specific noise (there's a lot of noise) that I'm referring to. If you know how to fix any of the other noises as well, feel free to mention it. While recording the video (with my phone) I moved it a lot to try and capture the noise from different angles but that didn't seem to make a major difference. Note that I am driving with the top up and windows up, the wind noise is just that bad. I recently did the spacer trick with washers to try and fix it and the noise came back 2 days later so I'll likely have to buy hardtop strikers. Another thing is that all plastic inside behind the cup holder is removed at the moment so cabin noise is a little bit louder than normal (not by much though). Also, I don't go above 5.5k in the video (never enter VTEC), most of the noise is around 2k-4k, more specifically around 3k. If I accelerate hard and fast or am in VTEC, most of the non-exhaust cabin noise is gone (the card sounds happier tbh), most of the noise happens when driving the car like a normal "not fun" person. With my earphones in, at about 80% volume the video is almost identical to how it sounds driving the car (very loud cabin noise).

As for possible causes, I've checked:
- Oil levels (I've noticed that sometimes low oil causes a somewhat similar rattle, but my oil levels are solid and I recently did an oil change)
- Motor mounts (flexed slightly while prying as it should, but did not move like how I've seen bad mounts move)
- Exhaust heat shield next to the engine for cracks (I didn't see any but I have not tried removing it yet)
- Heat shield around battery area (It didn't seem to have any give, felt secured
- Passenger seat and driver seat (tightened bolts on driver seat, passenger seat is removed)
- All interior plastics at or behind the cup holder (have not yet removed front dash)

Things I have not yet checked:
- TCT (I have this noise as well and will be sandblasting soon)

Things that I've heard made noise that I wasn't sure how to check:
- Fuel pump harness
- Trunk springs
- Exhaust bolts (I briefly inspected it and I didn't see any loose bolts)
- Clutch (I've got clutch buzz, but that's a different noise)

I'll try and see over the next few days if I can set up and mount a studio mic to capture the noise since the phone quality is not too good.

There are other times as well but these are the most prominent:
@0:14-@0:34
@2:00-@2:14
@3:04-@3:34
@5:08-@6:02
@6:38-@6:44
@6:55-@7:14

tohlenforst

I've found that the sound is most prominent right around 3k whether the car is moving or not. I'm going to try a little more investigating but if I can't get to the bottom of it I'll go ahead and record the sound with a studio mic like I mentioned and post it here.

Car Analogy

The air noise, and also since it seems like constant rpm, not varying, it sounds more like a recording from a small aircraft, not a car.

Advice is to fix the loudest issues first. It'll be easier to isolate the lesser volume sounds once they are the loudest.

But, since you said it sounds like its behind you, these things come to mind: (in no order other than stream of consciousness)

Pinion nut on diff loose (you have to drop propshaft rear mount to reach nut)

Propshaft cv joints worn, and chattering on decel (creates a similar effect as clutch buzz)

Fuel pump cover in trunk (its behind the grey panels. Caution, sharp edges. You can't see what you are doing due to stuff in way, can't feel what you are doing with gloves on. The amount of blood spilled when I removed and reinstalled this panel is horrifying)

Heat shields on right side muffler

Trunk springs (rule out by trying to reproduce noise with trunk open, and a rag or something stuck between them so they can't rattle)

Rear bumper mounts (not the plastic cover, the actual metal bumper bolted to car, under cover, under white foam)

Loose spare!

Spare tire tools (if they aren't safely ensconced in their foam cradles)

Gas tank heat/debris shield (under car, bolts to rear subframe)

Loose rear subframe brace (that wimpy U channel piece that you have to remove to drop exhaust)

Loose diff mount (especially the mounts that connect the front diff mount brackets to subframe)

Loose exhaust tip!

Loose rear plastic tray (interior, under softtop. Not clear if thats already removed)


If it turns out the noise isn't really behind you, there are a bunch of other things to consider.

tohlenforst

It certainly feels that way sometimes.

Thank you for the list! I'll try to check as many of those as I can tomorrow and throughout the week when I have the chance. Another update is that I found out that one of the noises was from the emergency trunk release wires vibrating against the trunk. Ironically, I figured this out by locking myself in the trunk and having someone drive around so I could try and pinpoint some noises. I'll go ahead and get that fixed or removed and then I'll try to isolate and tackle the next noise.

I've checked a few of the noises on the list (I need to update the OP to reflect this), but am not sure how to check some of the more complex noises such as anything pertaining to the propshaft/differential. I'm going to be changing my diff fluid soon within the next 2 weeks or so, so I suppose that will be the perfect opportunity to check those things.

tohlenforst

5' 7", 155lb.
I wasn't exactly comfortable, but there was more clearance than usual because the interior of my trunk is all removed at the moment (emphasis on not comfortable haha). Regardless, if I was 6' 2" 180lb. I would remove the spare tire and still try to shove myself awkwardly in the trunk. It's the least I could do after putting my car through so many years of hell and neglect .

Car Analogy

To check propshaft cv's, car in gear, e brake on, grab shaft and try and rotate it. See how play there is. Try and isolate any play on diff or trans from your assessment.

To check pinion nut, remove allen bolts that connect propshaft to diff, and drop down shaft. Then you'll see the big pinion nut. See if its torqued properly.

This would also be a good time to check one more item I forgot to include in the list. The brace that keeps propshaft from falling to ground if it breaks free from trans. Make sure its not loose and vibrating.