shuddering while stopped in gear

so my car is a 01 SS A4. Its pretty stock. custom cats and y pipe, hyperjunk tuner, K & N filter, poly trans mount, z06 rims.....

My issue is that I can feel some sreious feedback in the form of vibration and or shuddering in the brake pedal when I am in drive but at a complete stop. Im redoing the brakes (new calipers rotors and pads w full fluid flush) this week but I dont think it has to do with the brakes theyre just shot. feels like motion thats transferred from the rotation of the engine im just not sure of the exact cause.

To the point of me having to put the car in neutral to stop the vibration. I do have a poly tran mount. motor mount is stock not sure if its still good or not 120K miles later.

its strange it does it about 80% of the times i stop and only occurs once i have come to a complete stop. I thought maybe my harmonic balancer or motor mounts. I was hoping that someone with an A4 car had experienced this before and could lead me in the right direction instead of me throwing parts at the problem.

any help would be greatly appreciated. Anyone in the great state of Texas esp the DFW area that has info or does side work on these cars would be a great contact for me to have. Thanks in advance to any and all that reply.

Chance:Popcorn:

just a shot in the dark but check your accessory drive belt for slippage or excessive vibration

I can tell you my experience with the poly trans mount. My trans mount was broken, i bought the poly one and as soon as I started driving I had excesive vibration on the dash, shifter and middle area of the car. I check everything and no luck. Since it all started with the mount I decided to buy the stock one. The problem was solved as soon as I put the stock mount on it. Hope this helps.