I've got a 97 850R Wagon with 125K. Recently, I've been having a rather scary vibration from what I think is the rear-end of the car under repeated braking-- like if I was in traffic where I was stopping a lot. It is WICKED loud and vibrates the whole car.

The vibration is very constant -- like one frequency. It almost seems like the ABS is pulsating, but there is no feedback in the pedal. I tested the ABS theory by removing all 3 fuses with any reference to the ABS system so it would be inactive. No effect.

I changed the rear brake pads (I thought they might be faulty or something) and nothing changed.

I took off the summer tires and put on the winter ones (maybe something wrong with the plies in the tires) and nothing changed.

The tires are another problem -- noticed what seems to be tread separation on the drivers side front summer tire (Kumho Exsta 712) when I did the changeover to the winters. Going to have that replaced... It's the 2nd time I've noticed that! The previous one was on the original Pirelli PZeros on the passenger front side almost 2 years ago.

What do you think??? This is an interesting one.