2004 Mazda 3 Flapping noise from rear

HCARLSON74

MEMBER
2004 MAZDA 3
2.3L
4 CYL
FWD
MANUAL
97,000 MILES

I just got new tires and was getting a vibration at high speeds. So the 2nd time in the shop they figured out I had 2 bent rims (why did they not notice this when they put on the new tires?). Now, after replacing the 2 bent rims, I now have a flapping noise coming from the rear of the car that seems to go away at higher speeds (or the road noise blocks it out). It is definitely more noticeable at slower speeds (25-30 mph). This flapping sound was not there before the rims were replaced. I also did not have a high speed vibration PRIOR to getting the new tires. I am starting to wonder if the mechanic is not qualified :-/ or what the deal is.
Any suggestions are appreciated- thank you!

1 Reply

CARADIODOC

MECHANIC
33,916 POSTS

Bent wheels rarely get noticed on a spin-type wheel balancer unless the mechanic is informed to watch for something because the wheel / tire assembly gets covered by a protective hood when it rotates.

There's two things that can result in a wobble that wasn't there with the old tires. One is the tire is hard to remove and the shoe on the tire machine puts so much force on it that the wheel bends. That mainly applies to steel wheels but those days are pretty much gone thanks to the newer "rim-clamp" tire changers. The more common cause, especially if you have cast wheels, is the center part of the wheel starts to corrode apart and a chunk sticks to the hub. The wheel will spin perfectly true on the balancer, but when the assembly is placed back on the car, that chunk gets stuck between the hub and the wheel. That causes the wobble. That's not a competency issue. It's an experience issue. Every mechanic runs into this problem with wheels and brake rotors at some point in their career. Rather than just blindly replacing wheels, the proper approach is to diagnose the cause to know for certain what the cause was. Use a dial indicator to measure "lateral run out" on the car, and again on the tire balancer. If the run out is excessive and the same on the balancer, it's a wheel problem. If the run out is less on the wheel balancer, check for rust and debris on the wheel hub.

Without hearing the noise or being able to inspect it, my best guess is you're hearing the tire tread squirming back and forth for the same cause as that wobble. That is usually a lot more noticeable when the tread is wet and on sand or dirt on a paved road. Related to that, check if you're mechanic used a click-type torque wrench when he installed the lug nuts. No one uses an impact wrench anymore to tighten the nuts. We'll run them on that way, but using a torque wrench next as the final step is required by all shop owners to prevent a multitude of problems.