[LanceGT4]

When was your last alignment check? Wear on suspension parts?
After I had mine checked I still has some wandering. higher tire pressures helped. 36.5 front and 40.0 rear. (see tires below)
Check your motor and transmission mounts.
I'm not sure what the process is for the motor mounts:-( unless you remove them and check how much force it takes to move the support stud. Should be very stiff.
I just changed my motor mounts on my '99 C4.
Right one started leaking oil when I raised the rear end to put a 160 degree thermostat in.

Turns out the one that showed no signs of leaking was totally shot. With new mounts in place the car tracks better. Tire and road noise are reduced, with H&R springs and 19 inch wheels w/ Potenza RE050A's. The FabSpeed mufflers are also quieter at cruising throttle.

Let us know what you find. Good Luck.