Grinding Noise coming from the engine compartment!!!!

[Ash977]

Hey guys,
I did more testing last night. I made a mistake in my initial post. The noise actually changes as I rev the engine. So, I was driving about 50 miles/hour when I shifted the car to N. I still could hear the grinding. I kept pressing and releasing the accelerator to maintain a fluctuating RPM between idle, 600, to 1500rpm. The level of the grinding noise kept changing. However, the change was very gradual and small. Let’s say additional 15% noise at its max. I can’t hear the grinding noise when the engine RPM passed 2,000 as the exhaust and engine noise gets very loud.

Can this be an internal part of the engine (valves, intermediate levers, timing chain, or a tensioner)?
OR
External bearings (i.e. alternator, water pump, power steering pump)?

Any idea????

Thanks….




Let me start by saying I am addicted to this forum. I check the board at least few times a day. Having said that I tried searching the forum regarding grinding noise and read numerous threads on that. But none of them is similar to what I am experiencing.

This post is for a 2006 BMW X5 4.8is with 32,000 miles. When I pass approximately 40 miles/hr I hear a mild but not loud grinding/hissing noise coming from the engine compartment. It can be described as the grinding noise that brake pad and rotor makes when brake pad is at the end of its life but much quieter. So, tonight I took the X5 for a ride on a quiet highway and did few experiments to pinpoint the noise.

After gaining about 50miles/hour I did the following:

1- I changed the gear from D to N. Neither lower RPM (ideal RPM) nor the disengaged transmission alleviated the noise.
2- I applied the brake slightly while the car was in N. It didn’t help at all.
3- I turned off the climate control. By climate control I mean just the fan, AC was off the entire time. The noise was eliminated after couple of seconds. I would rule this out because after the vents were closed I just couldn’t hear the noise since it is not loud. I assume when the climate control is turned off, the vents that allow air in from outside close automatically and that takes a couple of seconds.
4- Lastly, while the transmission was in N, I turned off the engine and quickly turned the key back to position 2 to turn the headlights on again but the engine remained off. The climate control remained on, the entire time. As soon as I turned the key, the noise was completely gone with no delay. This is another reason why I would rule out the the climate control blower.


So, I guess I am looking for a system within the engine compartment that is depended on:
1- Speed, minimum 40miles/hour or more, (or that's when I can hear it thru the vents)
2- Airflow through the engine compartment, (I think wind acts as a medium to bring the noise inside the cabin)
3- The engine rev,


And it is NOT depended on:
1- Transmission gear position.


I thought of a vacuum leak, alternator, water pump, power steering pump, and AC compressor. But when I rev the engine while the car is stationary I don’t hear the noise. So, I guess I would rule them all out.

I thought about the climate control blower. But the grinding noise doesn’t change (louder or quieter) as I change the blower speed while the car is stationary or moving. And the noise is not present at all when the car is stationary.

1- Does turning off the engine kill the radiator fan? Could it be the airflow add additional load on the fan and that causes the grinding noise? Perhaps a bad bearing???? If the radiator fan is the reason how come it doesn’t make any noise when the car is stationary and the radiator fan is turned on????

2- Could it be the airflow from outside causes external load on the climate control blower to make that grinding noise? The noise is present whether I have the climate control on circulate or open to bring in air. If that, then why does the grinding noise disappear when I turn off the engine???

Sorry for the long write up. I would appreciate any help on this matter.

[Ash977]

Hey guys,
I did more testing last night. I made a mistake in my initial post. The noise actually changes as I rev the engine. So, I was driving about 50 miles/hour when I shifted the car to N. I still could hear the grinding. I kept pressing and releasing the accelerator to maintain a fluctuating RPM between idle, 600, to 1500rpm. The level of the grinding noise kept changing. However, the change was very gradual and small. Let’s say additional 15% noise at its max. I can’t hear the grinding noise when the engine RPM passed 2,000 as the exhaust and engine noise gets very loud.

Can this be an internal part of the engine (valves, intermediate levers, timing chain, or a tensioner)?
OR
External bearings (i.e. alternator, water pump, power steering pump)?

Any idea????

Thanks….

[Weasel]

The quick way to isolate if the noise is internal or belt driven is to simply remove the belt for a minute to test. (only for a minute or less naturally since the waterpump/alternator etc won't be turning) If the noise is gone with the belt off try spinning and shaking each pulley by hand to see it the bearings feel good before you put the belt back on.

[Ash977]

Thank you, I will try that…