Strange Intermittent Ticking from Engine Bay

Hey guys, new member here. A quick thanks to everyone on these forums; I bought a 01 Jetta TDI 3.5 years ago, and have used this site for many repairs and advice. There is a lot of good information to study up on in here.
I apologize for the long post, but I want to be thorough.

Some time ago, I started noticing a faint ticking coming from my engine during light to moderate acceleration, and occasionally during deceleration. The frequency is consistent whether I am in 3rd, 4th, or 5th gear, so I was able to narrow it down to being engine related. This faint ticking has evolved into a more harsh thumping, and I believe I can even feel it's vibrations sometimes.

The interesting thing is, it only does it occasionally. I have not been able to narrow down a cause or even the scenario for when it finally does make the noise. The only thing I have noticed is it only does it after the car has been at operating temp for about 30 minutes.

My only thought is the original injectors and nozzles that now have 262K on them.

I have not noticed any significant performance drops, and I am still getting good fuel economy at about 51 mpg. I do get some smoke on a cold start-up, but my glow plugs are wired on a push button due to some other issues. So I am assuming that is what is causing the smoke.

It may be worth noting that I have replaced my cover and QA seals, as well as the main head seal on the injection pump about 4-5K ago.
I also just replaced a stuck thermostat that was not letting me reach operating temperature. During a 50 degF day, I would top out at 150 degF. I am now back to 190 degF, so I am guessing that is why I am getting more occurrences.

I am considering pulling the injectors out of my 99.5 project car that has a broken timing belt, and sending them to Kerma to be rebuilt, calibrated and some new nozzles put on.

Any thoughts on this issue would be appreciated.

So this noise only occurs when driving? Can you get it to occur just by revving the engine up in the driveway? When said ticking occurs, do you get any smoke out the exhaust?

I have not seen any smoke while the ticking was present. And it comes and goes, so I have never been able to make this noise on command.
Also, it only seems to happen around 1600-2200 RPM

Almost sounds like the hydraulic lifters aren't staying pumped up. Search out a few videos of ALH lifters and see if the noise sounds the same. I changed mine out at 323k, changed the ones in my dad's car at 225k.

Failing DMF?

Thanks for the replies.

I am not ruling out a lifter related issue, but it does not make sense to me because it is intermittent. I would assume if it were a lifter, the noise would be more persistent.

And the car was converted to a 5-speed with a single mass flywheel, so the DMF can be ruled out.

So, you have at least 263 thousand miles on this?
In my personal experience on these alh engines...now owning three with two of these I totally rebuilt: I have found that lifter noises on these are often NOT consistent.
And, after seeing the carnage other people have experienced with lifter failure, I am now fairly quick to electively insert new sets of INA lifters when a question exists....esp with this many miles.
What I personally would do (feel free to see it otherwise): I would buy a cheapo oil pressure tester kit from the red army (harborfreight) and test the oil pressure at the filter housing and see what you have got.....duct tape the gauge on the windshield bottom and drive around the block with it. That way, you KNOW what you have got.
You did not know the car from new...so, there is the potential for all kinds of stuff...even little stuff like an oil bottle aluminum foil dropped into the engine and now sits on the screen occluding the pick-up to a degree.
For $85 at 263K......a set of new lifters is NOT "wasting" money.
On the older 1.6 engines with hyd. lifters, I have seen times when the little oil galleys in the head would partially occlude....and was "repaired" with a total disassembly of the head and thorough rinse-out of the head.
You need to spend more initiative to determine where the "sound" is coming from. Readers can't work miracles.
Edit: also, after heating the oil in this engine, the potential for lower bearing pressure-loss will be more evident. Your problem, as stated, becomes evident with apparent warm-up. For me...oil pressure test is a "go."

I have a set of Bosch gauges on my column. Oil pressure and boost. On a cold morning on start-up, I normally run around 75 psi. After I get to operating temp and the oil gets hot, at idle the oil pressure will stay around 20 or slightly under. Normal acceleration and rpm's will put me somewhere in the ballpark of 30-50 psi.

I'm assuming to replace the lifters, the camshaft must come off. I don't see how you would be able to get the space needed with it in.

For anyone who may still be following, or interested, I've had some new developments with this noise.

Until this week, I have not heard it since the beginning of this thread. Then I headed to class one morning and it started as soon as I began to move. I could tell it was definitely wheel speed related, but still linked to acceleration. I would have bet money that the first noise I mentioned was consistent with engine speed, so I am not 100% convinced that these two noises are the same. But, nevertheless, they sounded similar.

It sounded to me like the CV joint. So I inspected the bolts, because I have had problems with those suckers backing off and coming loose. They were tight. But while I was in there, I noticed that the drivers side engine/transmission mount was moving a lot. I jacked up both sides one at a time and spun the wheels to see if I could replicate the sound, but with no success.

So I slapped on a new mount last night and took it for a test drive and the noise is gone. I guess the mount was just wore out enough that during acceleration, it would let the engine move enough to misalign the axle and make the CV joint mad enough to complain.

Still have no idea why previously it took the car warming up before it sounded. Maybe engine heat warming the mount material and loosening it up? That, along with silence until all of a sudden one morning becoming so persistent, is perplexing.

Maybe these two are unrelated, but I guess I will just have to wait and see.

Thankyou for the update; glad you found the problem.

Well the noise came back. With a vengeance this time.

About a week after I put on a new mount, I noticed it again, and it progressively got louder. Acceleration would give a solid thump, but when I would let off, it sounded like something was about to come through the floorboard. That along with turning noises and a BAD vibration pointed me towards the right inner CV joint.

I've known that the heat shield has been broke off for a while, but I guess the heat from the turbo baked the boot and let it shrivel up and tear. There was very little grease left in there, and even it was dry and crumby.

I replaced the axle with a cheap Cardone brand until I can rebuild the old axle with joints from IDparts. For anyone who might wonder, I can definitely feel a difference between the hollow shafts and the solid ones. There is a subtle buzz when the axle is loaded. I can feel it through the pedals, but it's bearable.

I still have no idea why replacing the mount temporarily solved the issue, but at least I have a new mount on. But for now, I guess i'll keep driving it until something else breaks!