Model 3 thunk noise in rear

Model 3 thunk noise in rear

Anyone have any idea what this noise is? I just spent hours at the San Rafael Service Center, second time and they can't find anything. I'd kept a spreadsheet for weeks detailing what and when, and even managed to do a sound recording. The challenge for them is that it's occasional, they can't reproduce it. The thunk sounds as if originating in the rear, left, near the charging port but noises in cars are notoriously hard to pinpoint. It occurs occasionally, driving slow, turning left or right, sometime fast and straight, almost always smooth roads, different temps, different SOCs. But I can't reproduce it reliably. I've emptied the trunk, folded the seats down to check hinges, pounded the floor and it's driving me nuts. I'm going back to San Rafael SC next week and we'll swap cars for a week but, I'm hoping someone in the Community has experienced this too!

Bighorn | November 10, 2019

It's not the supercharging, altitude-changing, or flexing thunk of the battery case?

AlasCon | November 10, 2019

Thanks Bighorn but nope, not it :-(

Bighorn | November 10, 2019

Sorry, now I've listened and clearly it's not. I don't know. Sorry. | November 10, 2019

I've heard quite a few sounds and this is a new one. Sorry, I don't have an idea of what it may be.

jimglas | November 10, 2019

trunk monkey?

M3phan | November 10, 2019

So I’ll describe what I hear: The first sound is a thunk, the second and third noticeable sounds are like a repeat but at a lesser frequency. Like something with a fixed end flopping it’s loose end against something and slightly bouncing. Has the SC opened things up through the trunk, backseat and rear floor area?

Bighorn | November 10, 2019

I agree, I thought maybe a suspension bounce attenuating, but it doesn't really fit the story. | November 10, 2019

Does the sound get louder if you open the windows? Might help identify if it's outside or inside. I remember on the early refresh S, on a few cars, the front plate came partly detached. It would flap in the wind and make an odd sound you could hear in the cabin at times. Thinking about it now, check the rear plate if it's attached properly - maybe it's flapping a bit?

Magic 8 Ball | November 10, 2019

The waveform shows it dampens quickly (each "pulse" shows a spike followed by a smaller "echo"). There are three events that are repeating but getting smaller in amplitude each time. Is it always in threes? How frequent is it (have you been able to get it to make the sound with repetition) or did you just get the recording by chance?

Mr.Tesla | November 10, 2019

I think I remember someone had a weird thunkity-thunk, and found he had a small rock bouncing around in an HVAC vent. Can't remember the details. I think it was something near the floor in the back seat area? I recall he got desperate to get it out and "launched it" up a steep hill, so it would fall down to where he could reach it. Fuzzy memory territory here.

Otherwise, try checking the HVAC inlet under the frunk cover. (the pop-off cap over the battery and reservoir tanks)

Mr.Tesla | November 10, 2019

Someone else had a rock bouncing around between the body and the composite covers in the one of the front wheel wells.

hpatel072 | November 10, 2019

alascon I have been hearing same thumb noise coming from either under the seat or rear bottom of the car. I have service appointment coming soon.It is fratrating when you hear that noise but how do i let technician hear.

AlasCon | November 11, 2019

Thanks so far guys. @M3phan, they have stopped short of opening things up ("we may have to take the complete rear end apart" they said) and haven't done that - yet. @TeslaTap, all solid on the front and rear plate ends. @Magic8Ball, not always in threes, sometimes just a single thunk and I got the recording by driving around for a week holding my iPhone in my hand with Voice Recording on, music and even fan off, so lucky recording indeed. I've read all the forums on rocks, A/C and even battery sheathing etc but none of those seem to be it. And I can't get it to repeat despite tearing up parking lots and crisscrossing winding streets in neighborhoods. And that's the problem for the SC: the old "mechanic can't duplicate customer report". I am switching cars tomorrow for the week with an AC technician and hopefully they'll hear it and figure it out. @hpatel072 agreed: SO annoying on a $60k+ car! I'll report on what I find out from the SC after this week.

Magic 8 Ball | November 11, 2019

@AlasCon It think we may have the same thing (ours is usually a single thunk). Ours is fairly predictable in that it happens more in cooler temperatures backing into our driveway and going down a steep left hand hairpin turn. It happens in other spots as well. I am pretty sure it is the same piece of battery casing sheet metal that flexes to make the noise in supercharging but instead of heat/pressure there may be a different cause of making it flex. Ours is not loud and does not happen often enough for me to be concerned.

There is a long standing theory that this is related to a manufacturing change linked to flufferbot retirement.

Bighorn | November 11, 2019

Yes, that's the battery flex in your case, which this is not.

larjam73 | November 11, 2019

I had almost the same problem last week. We were driving in the Blue Ridge mountains. The thunk sound seemed to come from the left rear, especially when we were on a curve, and driving fairly slowly. It happened just before we arrived at our destination, and the next day about 30 minutes after we left. It has not happened since. My first thought is that it is related to atmospheric pressure changes or temperature changes.

Bighorn | November 11, 2019

The flex associated with pressure imbalances of temperature change, altitude change, and physical torquing is well known and addressed by a service bulletin. This thread is totally unrelated per the OP.