Another strange noise thread

[damnbiker]

I've done some searching but could not find anyone with the specific sound I am getting.

I had $27k worth of crash damage on my 2014 S4, and got my car back just before new years this year. Along with the repairs, I had the shop throw on a new set of Michelin PSS because the OEM continentals were loud and at the wear bars. Car currently has 15k miles, 3k of which was from after the accident.

Since the repairs the PSS tires were night and day compared to the OEM tires and the car drove great and super quiet freeway cruising. In the last few weeks, though, I've noticed a bit of humming on the freeway. Its about the frequency of the freeway drone american v8 trucks get with a bad exhaust. Its fairly faint, and disappears with the radio at volume levels of "8" and above. I can "feel" the same humming noise through the gas pedal. The strangest thing is tha it ONLY happens at EXACTLY 73-76 mph. If I drive outside that speed range, I hear nothing. It happens on all pavement surfaces, more noticeable on quiet smooth asphalt. No change with side load.

I first looked for tailgating trucks/SUVs LOL....That wasn't it since it happens when I'm the only car on the road.

Next explanation is tire noise. I always seem to get visible heel-toe tread block wear on my audis after 2.5k, so decided to X rotate to reverse the wear like I did for the OEM tires. This did not fix the noise.

I know, you are probably thinking wheel bearings, but i did my best to check for play while rotating tires and found none.

About the same time I noticed the freeway noise, I also noticed that under moderate or harder braking, I can hear and feel "scraping/grinding" during the last few MPH before coming to a stop. Smooth at higher than 5mph. Not sure if its related, or maybe another sign of wheel bearing failure?

Any ideas?

[Sceanzo]

Is the humming noise throttle dependant? As in, does the throttle have to be pressed to hear it? Can you put it on cruise control between 73-76 and get it to do it the entire time?

[damnbiker]

Throttle independent. I can coast down from 80-70mph and I can hear/feel it as the car slows through that 75mph zone. Same for acceleration. If I gas it hard enough the exhaust drowns it out.

Totally stock except APR ECU and TCU tunes + pulley since 5k miles

[Sceanzo]

If you can feel it through the pedal, it leads me to believe it's around the pedal area of the car. This car is drive by wire so nothing but wiring harness is connected to it AFAIK. Possibly a heat shield vibration.

[Fourcircle]

Maybe a harmonic vibration at that speed. Perhaps try changing the tire pressure up + or - a few lbs, see if it continues. Also, some Quattros will produce a vibration at that speed in the drivetrain. I had a 13 A5 that vibrated at exactly 74 mph that Audi first blamed on the tires and wheels but later said it was a 'normal characteristic' of that particular car's drivetrain. I suspected it was a combo of the A5's 2.0t mated with their 8 speed auto tranny. My newer S4 is smooth as silk and I too run the supers. Good luck sorting it out. You are under warranty so I'd be taking that puppy in. Let Audi sweat it out.


FourCircle

[damnbiker]

Thanks for the replies guys. It does seem more like a resonance.

I'm currently running 39f/37r pressures and mostly drive alone. On REALLY hard corners I can roll the front tire a bit past the arms of the Michelin man tire roll indicator, so I'll try upping the pressure 1psi to see if anything changes.

I'd like to avoid a dealership visit since I'm flashed.

[damnbiker]

I've tried changing tire pressures up and down a few psi but the resonance is still here. I can actually feel it in the doors and center armrest a bit too.

Is there any other way to check a wheel bearing besides lifting the car and trying to rock the wheel?