Thoughts on this noise?

[slandis]

I've been trying to track down this noise since I purchased the car last fall. Its pitch is not speed or RPM dependant, but it can seem to be louder at times when driving. Most definitely not coming from the engine bay but rather rear of the transmission. It's loud enough that it's bothersome at 70mph on the freeway. Any ideas would be appreciated!

Setup: 1999 540i chassis, S62 swap w/LSD

Video

[DennisG01]

I'm not a pro, so maybe others can give some more specific advice... but to my shadetree ear, it sounds like a drivehsaft bearing. If you can put the car up on ramps, then slide under and start squirting bearings with WD40 (or even water), you might find the culprit. If you hit it just right the noise will disappear for a short time. I've used this trick on belt pulleys and it works very well.

[pleiades]

Driveshaft isn't moving when the car is parked.

slandis, what clutch/flywheel combo are on this car?

[slandis]

I would assume the stock setup from a 2003 M5 as that's where the drivetrain came from but I didn't own the car during the time-frame in which the swap took place.

[pleiades]

Judging from the video/audio, it sounds internal, but have you been able to rule out anything on the outside of the engine vibrating, like an exhaust heat shield? On my m52TU, the two small flat heat shields above the exhaust manifold and also an exhaust bracket that had loosened from its mounting point beside the gearbox have been noise makers in the past.

[DennisG01]

Driveshaft isn't moving when the car is parked.

Ummm... yeah... Thanks for the correction - I totally spaced on that one!

It still would be a good idea to get under the car, though.

[slandis]

Judging from the video/audio, it sounds internal, but have you been able to rule out anything on the outside of the engine vibrating, like an exhaust heat shield? On my m52TU, the two small flat heat shields above the exhaust manifold and also an exhaust bracket that had loosened from its mounting point beside the gearbox have been noise makers in the past.

I have basically ruled out anything in the engine bay. The noise is simply not nearly as audible from the top or underneath when listening from the front of the car. This has been quasi-verified by a couple other folks who I've wrangled into listening to the car. My first inclination was definitely heat shielding and I have admittedly not checked each piece of shielding though I have poked around under while the car was running and nothing seemed to have muted the noise at all. I'll certainly keep looking at the shielding aspect.

[slandis]

UPDATE: Took the car out to the PNW BMW meet in Chehalis today and it died as I entered the lot. Cranks, fires up, then immediately dies. Had to tow it home. Thinking it might be the fuel pump or the evaporate leak down pump (perhaps even the source of the noise?)

[JPR10]

UPDATE: Took the car out to the PNW BMW meet in Chehalis today and it died as I entered the lot. Cranks, fires up, then immediately dies. Had to tow it home. Thinking it might be the fuel pump or the evaporate leak down pump (perhaps even the source of the noise?)

That would explain the noise being audible from where you filmed vs. being under the hood.

[Ed CT]

It'll be interesting to see if it is indeed the fuel pump. Then we can all use that vibrato noise in your video as a prelude to pump failure.

[slandis]

I have ordered a fuel pump. I'll certainly report back with the results! I'll probably order a fuel filter while I'm at it as well...

[slandis]

Alright... new fuel pump installed. The car fired right up no issues (whew!) but the noise persists, possibly even louder now. However, with the seat removed and the ability to put my ear right up to the pump it is most definitely the source of the noise. My next theory is that perhaps I have a partial fuel filter blockage resulting in the pump having to work overtime. Fuel filter will be here Tuesday so I'll remove/replace and see where I sit.

[DennisG01]

Is it louder BECAUSE the seat is removed? Meaning, normally the seat acts as sound insulation? Is anything loose where it mounts?

[slandis]

Is it louder BECAUSE the seat is removed? Meaning, normally the seat acts as sound insulation? Is anything loose where it mounts?

It seems louder outside the vehicle. It's definitely not anything that's loose and is the pump howling/vibrating. I got my ear right up to the sending unit to take a listen and to my admittedly untrained ear it sounds like the pump is vibrating and it's resonating through the mounting bracket to the tank itself.

[DennisG01]

I've never replaced one, before, but what I meant is could the mounting bracket be loose or cracked? How is the mounting bracket secure to the tank? Is it welded? Maybe a weld broke? Again, I'm saying this all without ever haven physically looked at one - just what it "sounds" like it could be from experiences with similar things in the past.

[slandis]

I've never replaced one, before, but what I meant is could the mounting bracket be loose or cracked? How is the mounting bracket secure to the tank? Is it welded? Maybe a weld broke? Again, I'm saying this all without ever haven physically looked at one - just what it "sounds" like it could be from experiences with similar things in the past.

Oh, yeah I see what you're saying. I'm unsure about the mount situation.. I'll have to siphon the gas or run it low enough to fully see what the pump carrier locks into and its current state but it's definitely a possibility. Fuel filter is on my doorstep so if that doesn't resolve the noise then I'll move into the pump mount next. Thanks for the suggestions, I really appreciate it!

[DennisG01]

Although I'm skeptical, I've got fingers crossed for you that the filter takes care of it!

[slandis]

Got a chance to replace the fuel filter tonight and I'm happy to report that at least during an initial testing period the strange noise has disappeared. The filter on the car was dated 10/98 meaning it was 19 years and 120,000 miles old. As an afterthought today I remembered the jet pump that equalizes the gas levels inside the tank and figured that would be my next step but it appears I won't need to go that far (yet...)

Thanks to everybody who offered opinions and ideas!

[DennisG01]

Keeping fingers crossed - but glad to hear that sounds like it was the culrpit! Speaking of filters, I've still got the original on mine - probably should replace it. If for nothing else, it's good PM and most likely past it's "due date".

Do you think maybe the filter was creating some backpressure to the pump? Meaning, if fuel wasn't flowing through easily (obviously it was flowing enough for the engine requirements, though), could there had been a "buildup" of fuel on the output side of the pump , creating some type of turbulence inside the pump? I don't know if I'm explainging that correctly.

I do know that, from the marine world and speaking of boat props, that cavitation (small air bubbles form on the blades that actually explode and make noise) can develop when a prop doesn't have clean water on one side or the other of the prop -- or a rough/damaged blade surface... although that doesn't seem like it applied here since the sound got louder with the new one. However, maybe there was some pump damage from running like that for a while and it was quieter because of the damage. Meaning, it started louder, but the damage, over time, actually caused the noise to lessen. It might be interesting to see the inside of the old pump and the old filter!

[slandis]

That was my theory as well regarding the back pressure causing the pump to work harder all the time. We'll see if it holds out as I'll be driving the car tomorrow.

I'm not sure if I want to use any kind of cutting or grinding tools on these items but I agree it would be interesting to see if there's anything strange going on inside them. :-)

[DennisG01]

No, you definitely don't want to use anything that will cause sparks. However if this things are aluminum, low speed cutting is generally safe. You may be able to snip it open with cutters. Also... certainly let it air out for a while! If you're so inclined - send 'em to me - I've cut many boat fuel filters open.

Good luck - hopefully the sound stays away!