Vibrations

So I have a MK4 VW Golf.
When I drive with the gas pedal depressed or when the car is coasting, at 1800 rpm only and only at 1800 rpm does the car start to make a vibration type of sound. Almost as if there is something touching but there isn't anything touching that could be found.
It can be recreated by simply depressing the pedal, when driving only, and slowly releasing it, you can then feel something as if there is either grinding or vibration. What could an RPM related vibration/resonance be related to? note: I have replaced the automatic tranny, mounts, front bushings.

Check your motor mounts and dog bone first. I would also take a close look at your alternator pulley and check your DMF. I had both go bad at the same time so I replaced the pulley first and then had to do the DMF.

Do you have aftermarket drive shafts?

Inner CV joint is a possibility. If you have VCDS I'd run some logs to rule out any engine-related issues.

Try revving it to 1800 and try to steady it there in neural with clutch out, does it still do it? could be intake manifold full of crap.

Wow did not expect such fast responses! Thanks!! I have aftermarkets shafts, I even had it tested with used OEM version, same thing.
I will double check my mounts again, they are new. but you never know. Intake manifold is clean
As for the pulley. maybe that's an issue. I'll let u folks know after I get that checked out in a couple of weeks or so.
FYI the car is an Automatic trans, 1.9 Golf TDI Thanks

Could be a wheel bearing going out? They seem to be rather rpm sensitive at first. You'll know sooner or later

Can you cause this in ANY gear?

My wife's car recently has exhibited (post clutch install- axles disturbed) a shudder when hammering on it in fifth gear at around 1,800 rpm, and lasts only till about 2,000 rpm. This is maximum torque/stress. I'm pretty convinced that it's an inner CV joint: the conditions that cause this behavior aren't very common in which case I'm letting it ride.

Well I had no luck with the vibes however, now I noticed as a definite thing. When I got my serp belt replaced the shop I went to said it was my timing belt area that a squeal was coming from and it may be a loose pulley or something. They don't work on vw timing belts but I booked a shop in Vancouver for this next week. I am thinking maybe that's why my car was vibrating,... gosh hope nothing got screwed up with the harmonic balancer when I had the timing belt done by the stealership. I remember it was vibrating after that when I got it done. ugh. I'll give you all the update after it's done.

I've seen this with an out of balance wheel. Weights can fall off.

Well I took the car in for my radiator fan to be replaced it was dead.
I mentioned the issue of vibration only at 1800rpm. It's definitely felt more when the gas pedal is depressed and can stay at that and when the pedal is released it sort of goes away... he said he couldn't be sure what it could be. I also noted as I had said when coasting...just at that rpm. nothing is touching. So I will probably keep on driving it until something happens to it.... burn. It seems more pronounced under load.
The things I have had done with this car in the order I remember best
1. control arm bushings (audi tt) replaced as they were shot
2. turbo removed, put back in as the actuator was fried
3.flex pipe redone under the car. nothing is touching though...
4. all three engine mounts replaced
5. transmission (automatic) replaced
6. front axle replaced, just one of the sides.
7. timing belt and serp belt replaced at required interval
7. oil changed at required interval.

Ordinarily, with vibration (presents as steering wheel shimmy) in the front with depression of the go-pedal, I'd say the inner CV joints need to be swapped or replaced. But in this case, I'd go with #6 being the culprit. Particularly if the problem showed up after the half shaft was replaced with an aftermarket one, as these (aftermarket half shafts) have been shown to be problematic.

If you have done this test in gears other than 5th, and seen the same thing at the same rpm, then having the dealer play with the harmonic balancer could also be a source. Unfortunately, even dealerships are plagued with people in the service department that should not be allowed to touch tools within shouting distance of a mechanical device of any kind.

Good luck,

PH