Wierd growling - loud humming noise --> HELP

[LuvDaDiesel]

I have been experiencing a sound that has increased in either noise or amplitude over the past couple of weeks. RPM range 1500-2000, no other time - any gear. Something clogged? Mileage has slightly dropped from 48-45mpg. any ideas?

 

[CARTMATT]

DSG, manual? Where you think its from? Sound mechanical, airflow, pulleys or belts? DMF? Does it dramaticly reduce speed when let off gas more than norm? Not much info!

 

[LuvDaDiesel]

Sorry, 5-speed '06 210,000 miles. It drops off when acclelator is released and also when RPM is increased above range. Additionally, I do have the EGR actuator (my terminology) leak which hisses and leaves soot in the engine bay. No other series modifications - new SMF and clutch when DMF failed. CV jonts replaced 50,000 miles ago, front wheel bearing replaced about 90,000 miles ago. Last but not least, the sound seems to be coming from the the driver's side, but I have not been able to specifically identify the source.

 

[CARTMATT]

Has the cam been checked or replaced? Even though filters may have been done recently, one bad tank can kill a fuel filter. Ive had them make car run goofy at that range and feels as if turbo is acting up. Does it jerk or chug when noise comes on?

 

[LuvDaDiesel]

Filters changed within the last 2 weeks, sound still remains. I was concerned about the CAM so I had the opened it up at the same time. The cam had some lsight wear tracks on one lobe for both cylinder 2 and 4, but in my uneducated opinion "not too bad". Additoinally, cylinder 3 had a lobe that the tip was showing a slight amount of wear and it looks as if there might be a small "dent" or two on it with a bit of a sharp edge. At over 200K I didn't think it was too bad, but open to the thoughts of others. NO jerking or chugging.

 

[CARTMATT]

If the chamfer is gone and its a sharp corner, lobe might be further that you think. If you do find the problem as something dif, still sounds like time for cam and lifters! Might as well do TB and waterpump if in there in future. Search cam threads to see what symptoms are, may prove or dismiss cam.

 

[LuvDaDiesel]

I'll poke around abit. Timing belt and H20 pump, etc. was changed @ 195,000 - second time. I'm getting quicker with each service. Thanks.

 

[jdhunt0]

I've had the same thing for over a year now. I went from getting ~45 mpg to ~39.

 

[LuvDaDiesel]

Well, here's the plan........I chatted with a couple of my buddies that have the same car, same year and they support the theory of the cam. The suggestion by CARMATT that the wear is further than I might think seems to be right on the mark. Planning on ordering the Camshaft Kit from IDparts and I'll let the group know how it goes and if it "fixed" my problems. Probably not this weekend, but in the near future.
Thanks everyone - happy "rattlin".

 

[jdhunt0]

I'm not saying it's not the cam, but a new one did not help my car.

 

[BMac]

Do you notice the growl more when the car is slowing down (off fuel) or when you are accelerating?

Cheers

 

[curovo]

Timing belt tensioner? I had similar behavior from a failing one on a gas A1... rpm dependent & dropped off when I let off the gas, presumably because it eased the load on the belt > pulley > bearing.

 

[LuvDaDiesel]

Interesting. I have had mention of a/c bearing failure, but when I took a look at that, nothing seemed out of the norm. When I get the chance, I will pull things apart a bit more and look at the tensioner. Thanks.

 

[MyAvocation]

How did your lifters look on the cam inspection? That's what you really need to keep an eye on. I had significant lobe wear on 2 of them at 200K, but surprisingly low lifter dishing. Didn't expect it to survive to 300K, so changed it all out as part of the TB job. At least on mine, I never heard any loud humming, so I question whether it's the cam.

Here's an easier test: Remove the serpentine belt and test the clutched pulley, which should free-wheel in one direction. The clutching tends to fail after high mileage and they always make strange noises within an RPM range, that tends to vary per person. If it tests fine, then while you have the belt off, go for a short spin to see if humming ceased. NOTE: You'll need VCDS to clear numerous codes, so ye beware. At the very least this can narrow things down alternator, AC pump and tensioner.