Weird low reverb sound while coasting.

Hey all, Attached a YouTube video for reference. Might be hard to pick up, but when I coast in 2nd (from 3m down to 1500/clutch-in stop), I've noticed a really low reverb sound. Kind of like a "wub wub wub" that is in the background of all the other noise. The sound seems tied to engine speed or something rotating. It seemed potentially gearbox related because it doesn't make that noise with clutch in or when idling or when revving through the same window, but shifting isn't difficult or strained. However, it also seems to be coming more from inside the cabin versus trying to hear it outside by poking my head out while driving. Also can't hear it while accelerating. Only seems to show up while coasting at lower revs - something like backdrive. Not sure. Also, I've noticed its apparent in 1st gear starting at around 4k. 3rd gear it's harder to hear but still there around the 2500 mark. Higher gears I can't really hear it but I'm going way faster so there's a lot more noise. I want to say I just noticed it morning - and is present cold or warm. But I can't say for sure if this sound existed the whole time - I don't think it has. I did take a very spirited drive on some TX back roads (~300mi) pushing the speedometer and engine a few days ago. Was a blast and the car operated like a champ the whole way through. I don't feel like there's any weird signs when pushing the car above 4k; feels like normal to me. The car in general seems to run normal despite that lower reverb sound. To my knowledge on the drive back and city cruise the following day, I don't remember hearing that sound. Feels like it just started on today's morning drive. Tried searching forums for this kind of sound but most posts are about high pitched whining. https://youtu.be/7qI4PbqS9HQ?si=zgiBtJReIF2CpDBd Low reverb sound

Hard to tell from the video but when is the last time you replaced your tires? The "wub wub wub" sound I had on my truck was from under inflated tires and they were wearing oddly which caused the sound. I would start there and check your tire pressure and see if the sound remains.....

Quotes source post: 19642702

That's a valid reason - I will check tonight when cold. However, the noise goes away when clutch goes in (engine disconnected from the wheels) so ii didn't think it was tire related. The tires on the car are getting to the end of their year limit (but not worn) and with these roads & driving I've noticed I will need an alignment soon.

Update: Got new tires (man i love them), but still hearing the sound in the same speed range. Discovered my motor mounts are pretty shot, so ordered parts to replace them. This might be the issue as well. Otherwise the car seems to shift/drive normally. Still perplexed.

Update: As a PSA for others potentially experiencing similar sounds. 2 individual Porsche-focused mechanic opinions: 1) Final Drive bearing issue. They flushed transmission oil and didn't notice any fluid concerns by the color. Recommended Transmission Rebuild 2) Doesn't seem like just a Final Drive bearing issue as the gearbox is incredibly noisy. The reverb noise is a bearing wearing out. Recommended Transmission Rebuild. With #2, we got the car on a lift running through a few gears and put a stethoscope up to the gearbox and the differential and the former sounds like a garbage disposal of glass marbles (where it should be more harmonious) and the latter was way quieter (more harmonious). Transmission fluid was incredibly thin and grey (almost like shavings were in it immediately) - and note this was 6mi after the 1st mechanic flushed it. I have doubts about what they put in there (oil & some additive) and recommended I drive 500mi to see what happens but it won't remove the problem just prolong it. Even when looking at the removed transmission fluid, that sample was quite watery as well. Very unusual but I don't know how trans fluid behaves when warm. Overall, I trust #2 more based on the work i've had done by him (went to #1 for the 1st time for this issue), and have driven the car home and stopped driving it until I go back to the shop for them to pull it out. All that to say is I never had issues in any of the gears, finding gears (upshifting or downshifting). Hence why it was determined to be more of a bearing issue on the output shaft.(going to differential). I'm waiting on a cost quote to know what this rebuild might cost, but ultimately won't know what is wrong with the transmission until a shop tears it down for a rebuild. Fingers crossed it's not a lot of repair, but it will be good to know what needs to be replaced. While the transmission is out, I'm going to be addressing a myriad of things: IMS, RMS, Clutch, Flywheel. I already replaced the AOS. Let me know if there's anything I'm missing. Engine is not coming out - so can't replace other things most posts mention. Overall, a bit surprised this car developed a transmission issue at this mileage age (75k). Perhaps a PO rarely drove it and the lubrication left some of the hard to reach spots in the transmission.

That�s too bad. Transmission issues like this are rare, but they do happen on occasion. Probably just bad luck, although if the fluid wasn�t changed in 20 years, well, it should have been. Would that have prevented the issue a long time ago? Hard to say. Sometimes it has nothing to do with fluid changes.