Grumbling Noise - What's Causing It?? TRANSMISSION

S

StudioWizard

Member
Los Angeles, CA, USA
Hey everyone

I recently acquired a 2005 2.5i with automatic transmission. It's got some issues and I'm slowly going through each one to get this car back into top shape.

The most pressing issue right now is that it makes some kind of "grumbling" noise when it's shifting from 3rd-4th and 4th-5th gears, especially if I'm driving very conservatively, which is what I'm doing 99% of the time because I don't want to push the car at this point. Sometimes, when I start noticing the grumbling, I speed up and it immediately reduces the grumbling and changes gears. The gear changing seems smooth otherwise. And the engine sounds really good, too.

I'm worried that this might be a VERY serious issue with the transmission, but I know it could also be a bunch of other things. I've had a couple of mechanics look at and test drive the car and neither one said anything about it. I think I'll need to drive the car with them in it to be sure.

Here are some things that the car for sure needs. Do any of these things sound like the potential cause?
Broken upper stabilizer bar (above the engine)
Suspension Control Arms cracked/broken (lower)
Engine Mounts Collapsed (both)
Spark Plugs Worn and Burnt / Ignition Coils Worn and Rusted

Here are a few things that were just fixed:
Fuel Injectors Replaced (all 6)
Engine Oil/Filter Replaced
Transmission Fluid Drained/Refilled
Differential Fluid Drained/Refilled

Here are a few other things that need fixing, but probably aren't the cause:
Engine Oil Pan Gasket Leaking
Crankcase Vent Valve Brittle and Cracked
Oil Line Leak - Vanos Unit
Engine Valve Cover Leaking

Lastly, 89 grade gasoline was used in the car for two or three fillups, then 87 was used for two more fillups until I was informed the vehicle needs Premium. The last tankful was 91 and will continue to be 91 from now on. The previous owner generally used at least 89 but usually 91. They're friends of mine and they bought the car in 2019 and barely drove it during the pandemic.

The car has almost 160,000 miles on it.

Any thoughts, recommendations and questions are greatly appreciated!

Thanks!

Paul
 
Was it doing it before the transmission fluid was changed? I'm assuming you are in the USA? It doesn't need premium. its set up to run on 91. It should say on the fuel filler cap.
 
Yes, I'm in the USA.
It was doing it before the transmission fluid was changed. It didn't seem to affect it once changed.

I'm confused by your statement that it doesn't need premium, but that it's set up to run on 91. 91 is premium, no? Or, are you saying that it CAN run on 91, but doesn't need to? The mechanic said it needs premium (he could be wrong, though).
 
Yes, its very much UK based but we do have a few members from across the pond!

We cannot buy anything as low as 91. Standard is 95, super is 97 or 98 and premium is 99.

UK cars make a fair bit more power than USA market ones.
 
Update: I drove the car today and really paid careful attention as to when the grumbling sound is actually happening. It's NOT happening during shifting of gears. It's happening just after it has shifted into 5th mostly and occasionally into 4th. It seems like it has to do more with the speed of the car because it's always happening at approximately 42-45mph (sorry I'm not sure what the km/h is). Also, it doesn't seem to do it in Sport mode or if I manually shift into each gear. So, it seems like it's not the transmission.

Does that narrow it down at all?
 
Holy Cow!! Premium in the US is 91. Wow! And the gas cap on my Z4 says it MUST use "Premium" 91. Haha! I never knew this. Is that much higher octane rating at least partially responsible for why gasoline is much more expensive in the UK than the USA? We're all bitching and moaning for gas over $5/gallon here.

Fun fact: I drove a Chevy Volt (plug-in hybrid) for 5 years and spent an average of about $200 PER YEAR on gas for that car. It was a fantastic car and I sold it for more than I paid for it mostly due to the supply chain shortage. Never thought I'd ever go back to a petrol vehicle, but here I am!


Rockhopper said:
Yes, its very much UK based but we do have a few members from across the pond!

We cannot buy anything as low as 91. Standard is 95, super is 97 or 98 and premium is 99.

UK cars make a fair bit more power than USA market ones.
Click to expand...
 
91 Octane in USA is equivalent to 95 Ron in Europe
93 Octane is equivalent to 98 Ron

and don’t even get into PON :D
 
91 Octane in USA is equivalent to 95 Ron in Europe
93 Octane is equivalent to 98 Ron

and don’t even get into PON :D
 
StudioWizard said:
It's happening just after it has shifted into 5th mostly and occasionally into 4th. It seems like it has to do more with the speed of the car because it's always happening at approximately 42-45mph (sorry I'm not sure what the km/h is).
Click to expand...

We do distances and speeds in miles here too.

Sounds a bit like the torque converter lock up clutch to me. Could be worn to the point where it's slipping slightly.
 
Hmmmm.

Can you try holding the gear in 3rd, and drive at 42 - 45mph?

It’s possible it’s not the gearbox at all - you might have an issue with something vibrating at road speed (maybe wheels balance or bearings)
 
matsmith749 said:
Hmmmm.

Can you try holding the gear in 3rd, and drive at 42 - 45mph?

It’s possible it’s not the gearbox at all - you might have an issue with something vibrating at road speed (maybe wheels balance or bearings)
Click to expand...


Excellent idea. I will try that today!
btw, when you say "gearbox", do you mean the torque converter since this is an automatic? (I'm a newbie to Z4s, so I'm not totally sure.)
 
OK, I just tried driving and holding 3rd, 4th and 5th in various situations. 3rd/4th is basically no problem, but 5th causes that grumbling especially at lower speeds (30-40mph) and going uphill. Even in auto mode, the car wasn't grumbling as much today.

Anyway, now I'm somewhat convinced that it's the motor mounts and other bracing/strut structures.
 
StudioWizard said:
Is that much higher octane rating at least partially responsible for why gasoline is much more expensive in the UK than the USA? We're all bitching and moaning for gas over $5/gallon here.
Click to expand...
No it's because the UK has, for all my lifetime at least, taxed the sh1t out of all oil-based products. Easy tax and gets them a LOT of revenue.

We don't do km/h in the UK, we still do mph and miles. But we buy our fuel in litres and measure weights in kg and grams.
So we buy 40 litres of petrol and then work out how many miles per gallon that will give!! :headbang:
Why? Because we are stupid and like to make life difficult! :D

PS: a US gallon is smaller than a UK one. :headbang:
 
UPDATE: I had my mechanic check it out as we test drove the car. He says it's definitely the transmission. I'll start a new post about dealing with this issue.
 
Pondrew said:
StudioWizard said:
Is that much higher octane rating at least partially responsible for why gasoline is much more expensive in the UK than the USA? We're all bitching and moaning for gas over $5/gallon here.
Click to expand...
We don't do km/h in the UK, we still do mph and miles. But we buy our fuel in litres and measure weights in kg and grams.
So we buy 40 litres of petrol and then work out how many miles per gallon that will give!! :headbang:
Why? Because we are stupid and like to make life difficult! :D
Click to expand...

See I can quite happily work in miles and metres don't ask me about yards. But Why do we use Stones as an appropriate measure of weight and when did Pounds and Oz not be good enough. Because of that ive gone metric :) height and weigh are now in cm and kg.
 
StudioWizard said:
UPDATE: I had my mechanic check it out as we test drove the car. He says it's definitely the transmission. I'll start a new post about dealing with this issue.
Click to expand...

I haven't got anything useful to add other than get an 2nd opinion from your mechanic as driving it until it breaks is a sure way of needing to buy a replacement transmission. Im all about that mechanical sympathy if something is making a noise it needs fixing but sometimes you need to work out the cost benefit to fixing vs leaving.

Is it a grumble like this ? That is a Torque Converter going. Specifically I believe it was the bearing in the Stator or Impeller. The noise comes from the mid front part of the car and can sound like its coming from the exhaust.
[youtube]2Uiaim_eDrk[/youtube]
[youtube]xKNXyjI6GJU[/youtube]
 
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