B9 S4 - Car making a loud humming noise…

Ana318

Registered User
Hi there, I have a 2018 S4 B9, owned it 2 years at the end of this month. No issues, other than a faulty wing mirror heater, done under warranty last November. I do a lot of miles at the moment commuting, upon average 100 per day. Today, from a cold start (in inclement weather) I drove 25 miles - not hard miles, just a sedate drive in D mode. After 20 miles I realised that the stop/start system wasn’t working and there appeared to be a very loud hum coming from the engine. However, there was an artic in front of me and I thought it might be that. When the artic turned off and the hum continued I pulled over and manually disengaged the ignition. Usually when I do this, the car stops and all noises (apart from quite a quiet fan) cease. Today the car continued humming and slowly wound itself down, it sounded a bit like a jet engine or a helicopter. The noise didn’t happen again on that journey, but the start/stop still wouldn’t engage - FYI the ac wasn’t running particularly fast, cold or hot, it was on number 2 fan @ 19 degrees. I went about my business for about an hour, returned to the car, no noise and s/s system operational once again. Drove another 25 miles without issue. Called Audi and booked it in to be looked at, but they have no availability until the 15th. I wasn’t too fussed as it seemed to have stopped anyway. However, this evening I popped out for a relatively short journey of 8 miles and it happened again. Temperature is fine, not any different to usual.

Any ideas?

I filmed it for the audio, here is a link to youtube -
 
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Ana318

Registered User
Hi again, this light has just appeared- is this still consistent with thermostat issues? Book is saying emissions system
 

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Hi again, this light has just appeared- is this still consistent with thermostat issues? Book is saying emissions system
That's just the standard "check engine" light, could be anything. Car you get hold of a code reader? Failing that any local garage will be able to pull the codes for you for a few quid, only takes 5 mins
 

hellodave

Registered User
Hi again, this light has just appeared- is this still consistent with thermostat issues? Book is saying emissions system
Yes, that's the next stage after fan noise.

I say this as an S4 owner on his third thermostat

If you have Audi assist it's worth calling them - may allow you to get the car booked in earlier.
 

Ana318

Registered User
Audi Assist (AA) chap came out. No fault registered and car not symptomatic. He refused to recover it, despite my video/photograph of faults. Told me to go back to Audi dealer ☹️
 

Ana318

Registered User
Yes, that's the next stage after fan noise.

I say this as an S4 owner on his third thermostat

If you have Audi assist it's worth calling them - may allow you to get the car booked in earlier.

Flipping heck. My Manufacturers warranty is up in 3 weeks. Yikes
 
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