Kalvin

I have a '97 1.8tqm with almost 145k on the clock. In the last couple months, its developed what feels like a driveline vibration in 4th gear at 55-65mph, 3k-4k rpm. No vibration above or below these parameters, or in other gears. Its not a steady vibration, its rhythmic - thrum..thrum..thrum. During this time, I've also done a bit to upgrade/tighten up my drivetrain :
AWE DTS
034 street density motor mounts
034 street density driver's side trans mount
RS4 pass side trans mount
Apikol rear diff mount

I searched and all I found was this:
"4th is the closest to a 1/1 ratio on your trans and so produces max power transfer. I think this may be causing the drive shaft to vibrate. It's something that can easily be checked. I've seen a few posts on the center bearing going bad."

So my question is, am I simply getting the vibration because I've tightened things up, or do I need to get my driveshaft or something in my driveline checked?

4Driver4

Sounds like the center bearing to me.