Drive shaft vibration? B6 Passat

I recently had both drive shafts replaced. On taking it out for the first drive, there is vibration in any gear starting 1900 rpm and fades away after 2000rpm, but will come back again at ~3800rpm. This vibration is felt through the pedals and steering wheel.
its not a 'diesel' vibration, it a higher pitch than that. BUT it has only started since the new drives shafts were installed!! I had the garage test drive it and they do admit there is vibration, but they investigated the area and mounts etc and found nothing out of place that could be transferring vibration, but the long drive shaft had a small amount of play in it.
There is no reason for it apart from the shaft, so I am having the garage change the shaft and hope this solves it.

Has anyone come across this before??

Is it based entirely on engine RPM?

Yes and the harder I accelerate the harsher the vibration, but its not at a low frequency as if the engine mount(s) were the cause.

VW OE or aftermarket shafts?

I am guessing after market

Your OEM Axles were replaced with cheap Chineseum axles..... Replace them with a quality OEM Axle and the vibration will go away trust me I just went thru this on my BRM.

Oh great

Well, bit of an update: Had the shaft changed and yes the vibration has gone, but there is something not quite right, but can't put my finger on it. It just feels different.
Anyway, I've had enough of the Passat for the moment, what with 4 new Goodyear F1 tyres, new front discs & pads, rear pads and drivers door wiring harness .

Reviving this old thread, as I have some observations on drive shafts and the quality differences.
After many months of using the suspect shafts, I bought some SKF shafts. SKF are a well known bearing manufacturer in the industry of high quality bearings. So I thought these would do the job: not too expensive at @ £95 for the long shaft and @ £75 for the shorter one.
I swapped them over and the slop had gone...but there was now vibration from 1900 to 2100rpm, any road speed! I was not happy!
On thinking about it, I had noticed the long shaft was a solid and not made up of a larger diameter shaft and stubs welded to each end. My theory is that the engine vibration carried through the gearbox and at a particular rpm, the shaft's natural frequency is the same and carried through the floor to the pedals!
So I decided to swap the old shaft over, but change over the CV joints which are better quality.
Not quite so simple! The inner joint was easy to to swap over, as it was held captive to the shaft with a circlip, but the CV outer joint would not come off the new shaft, I think it was pressed on as I could see no clip on the inner end, as the other did. So I've put it all back together, with just the inner joint swapped over, but I could see the quality difference. The SKF joint had three ball races pushed onto ball-shaped spigots, which made the joint very flexible. The old joint had three ball races, but they were fitted to a normal round spigot. This shows why the old shafts would be cheaper.
So anyway, I haven't had chance to test the car yet, apart from moving the car around on the drive, but there is no slop and couldn't feel any vibration, but time will tell.

Update....No vibration!! So the thinner shaft did pick up the vibration from the engine.

So bit of advise: If you have to replace your drives shafts, make sure the CV joints are of a quality manufacturer and the shaft is made up of a larger diameter than the ends which connect into the CV joints.