2007 R56 Cooper Hatchback; 128,000 miles.

For the past several months Cooper has emitted a “buzzing” sound at engine speeds of 1,900 to 2,100 RPM. The sound comes from the engine compartment in front of the passenger’s feet.

After asking around and asking the dealership I learned that long time ago BMW or Cooper or both put out a technical bulletin stating that on some models there’s a steel a/c pipe that at a certain RPM range “buzzes” as it vibrates. The fix is to send Cooper/BMW $125 for a weight that clamps onto the steel a/c line thereby dampening the vibration.

Sure enough, when I remove the front passenger tire there’s a steel a/c line around the bottom of the engine that makes a turn to the rear of the engine and on that turn is a fitting the transitions from the steel line to a rubber hose.

I bought the part. It’s a stainless steel weight, round, comes in two parts that bolt together to encircle the a/c line (imagine a doughnut cut in half across its face making two semi-circles. The part did not come with bolts – I picked up two metric Allen head machine screws, jacked up Cooper, pulled the tire, and bolted the weight to the steel a/c line.

BIG PROBLEM. The inner diameter of the weight is about 2 mm bigger than the diameter of the a/c line. The weight is supposed to be clamped onto the steel line 81 mm away from the steel/rubber junction. Because the weight does not clamp onto the steel line, it slides along the line, back and forth, rattling as it goes.

I removed the weight and fished out of my electrical junk a very long nylon zip tie. There’s a frame member next to the engine compartment toward the front of the tire. I passed the zip tie over the steel a/c line, around the frame member, and pulled it tight. The a/c line does not move.

That was two weeks and 150 miles ago - - the buzzing noise is gone, not a hint of it. I think the zip tie is good for now but no doubt it will deteriorate over time. I’m looking for a substitute for the nylon tie. I found a place on Amazon where I can buy 12 feet of stainless band and 8 screw fasteners to make my own hose clamp with which to replace the nylon zip tie.

 

Dynamic dampers are used all the time on autos. I think I would have wrapped the AC line with electrical tape to build up the OD and mounted that weight (unless you have already returned it).