Gas Tank Creak?

[heinzboehmer]

I've been hearing a creaking noise coming from the rear end when accelerating from a stop for a few months now. I initially thought it was some incorrectly preloaded bushing and kept putting it off until I started doing all the rear end work I had been planning. Well now I'm in the middle of doing all that work and found that the noise is actually coming from the gas tank. As far as I can tell it seems to be coming from the top of the tank.

I'll remove the two access cap things beneath the rear seats in the next couple days and poke around to see if I can find an obvious cause, but thought I would post here in case anyone had experienced something similar. I'll include a video I took of me pressing on different parts of the tank. The noise only occurs when pushing up on the driver's side and is loudest when pushing up on that hump.

Anyone have any idea what this might be? Appreciate any help!

[ZHPizza]

Bit of a long shot but if you haven't done it yet I'd cut the panel under the rear bench and check the top of the subframe mounts. I say long shot because that sounds like a dry rubber creak but I can't think of what would creak like that in that area.

Those mig welds like to crack and let the mount pull free.

[heinzboehmer]

Thanks for the idea. I did actually cut into there as I installed a Vincebar and the gusset cups. Spot welds had no cracks and even with the gusset cups epoxied and torqued (with a couple wheel bolts) the noise was still there.

Guess I'll have to disassemble some stuff this weekend to see if I can find the source.

[old///MFanatic]

Does the sound stop when the tank has different levels of gas? Make noises during dips in road like speed bumps?
I would suspect something with the gas tank filler tube/hoses.
Another spot is the rubber grommet that isolates the bolt on the gas tank straps. #4
https://www.realoem.com/bmw/enUS/par...MW-M3&mg=16#05

[heinzboehmer]

Does the sound stop when the tank has different levels of gas? Make noises during dips in road like speed bumps?
I would suspect something with the gas tank filler tube/hoses.
Another spot is the rubber grommet that isolates the bolt on the gas tank straps. #4
https://www.realoem.com/bmw/enUS/par...MW-M3&mg=16#05

I'm not sure if the noise varies with the amount of gas in the tank or not. Never thought the noise would be coming from there so didn't pay attention to that.

I don't think it's any of the rubber in the straps either. When I noticed it I removed the driver's side strap and the noise did not change. I'm planning on removing both straps soon to take a peek above the tank. Are there any hard lines I have to worry about before I drop the tank slightly?

[ZHPizza]

You should be fine if you just remove the 13mm plastic nuts securing the lines that run up towards the front of the car (fuel filter, return, etc). You can let that hard section lower down with the tank and the rest will flex. Should give you plenty of space to shine a light up above the tank and have a look.

Actually with the driveshaft in you won't be able to lower it much at all. Probably don't even need to do what I said above.

[heinzboehmer]

Great thank you. I'll update this thread once I find the source.

[Grke46m3]

Interesting. I have a similar creek when going over a driveway apron or just taking off from a dead stop sometimes.


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[DropTopKingM3]

Sub'd.

[Will]

Interesting. I have a similar creek when going over a driveway apron or just taking off from a dead stop sometimes.


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Is this from sway bar bushing? I changed my sways and didn't grease the bushing, squeaks with every little movement.

Not sure about the gas tank squeak. Maybe the rubber grommet that oldFanatic mentioned.

[ZHPizza]

Is this from sway bar bushing? I changed my sways and didn't grease the bushing, squeaks with every little movement.

Not sure about the gas tank squeak. Maybe the rubber grommet that oldFanatic mentioned.

I had the same issue. Sprayed the bushings with some silicone lube and watched it pull right into the rubber. Creaking was gone without even having to loosen the sway bar.

The noise definitely sounds the same, but the fact that he could just push on the fuel tank and get that noise tells me it's not the sway bar.

[heinzboehmer]

Sway and subframe are out of the car so definitely not that. I partially dropped the tank today and it turns out that the creak is coming from inside the tank.

I could squish it from the top and bottom and recreate the noise. Guess I'll be pulling the fuel sender to see what's going on inside.

[heinzboehmer]

Sway and subframe are out of the car so definitely not that.

Okay these were definitely not creaking when I was pushing on the tank because they were out of the car, BUT I think the sway bushings might have actually been the creak I was hearing when starting to move from a stop. I haven't looked inside the gas tank to try and find why its making that noise when squeezed, but I haven't heard the creak while driving anymore (I replaced and lubed the sway bar bushings when reinstalling everything).

I'll take a peak into the tank anyway just to make sure everything is good in there (probably won't for a few weeks though).

[discoelk]

Did you ever figure this or anyone ever figure out if this is related to the fuel tank? I have a rear end creak that only appears when letting the clutch out or going over angled inclination (like a driveway). My car has a similar suspension set-up and vincebar with gusset cups, solid subframe bushings, and subframe plates. I don't see any cracks anywhere and most of the suspension bushings/bearings are new with the exception of rear upper control arm bushings. The car has SDW RTABs and made the noise before and after the install. I'm fairly certain it's not subframe/RACP related. I can replicate the noise by rocking the car hard but it's pretty basically impossible to replicate on jack stands. Pushing on my tank makes a similar noise but I'm wondering if that's normal (and unrelated).

[heinzboehmer]

I'm pretty sure the creak while driving was the sway bar bushings. Fuel tank still creaks if I push on it, but I never hear it while driving, so I've stopped chasing the issue.