Vibration under braking

Pulsating brakes usually means a warped rotor.

 

YEP!

One thing - have you removed front wheels recently? Sometimes if the wheels are reinstalled and the lug nuts not evenly tightened, it will slightly warp the rotor. I had a Porsche 911 that every time it got new tires, the brakes would pulsate. Soon as I got home I'd break each lug nut loose and retighten them in criss/cross sequence using a torque wrench - pulsating disappeared.

 

I did get a brake issue on my 328 once that seemed to be a mild vibration.
But the more telling symptom was that the brakes scraped when off.
The 328 (and I believe 308) has "floating" calipers. (Pot on one side only; the caliper "floats" relative to the rotor to pull the other pad to contact.)
If they stop floating, you might be getting only partial braking on that wheel, or the brake could be slow to release.

Shortly after I bought the 328 (used), I had to have the shop clean up the caliper mounts so it would "float" properly.

 

Yes, usually a warped rotor or frozen caliper but by the time you actually start feeling this it has already begun to wear out your tie-rod end so after jacking it up and before removing the wheel check for play by holding front and rear of tire and rocking. Also check ball joint while your at it by rocking top and bottom.

 

Did you park it up wet? could be a chunk of pad stuck to the rotor.