My car has been sitting for about a month but ran fine when parked, I had just taken it on a six hour round trip maybe a week prior to it sitting. Yesterday when I tried to take it out I noticed a clunking sound immediately that is consistent with the rotation of the wheels, you can feel the clunk under the brake pedal if that makes sense and the sound gets louder when pressing the brakes. I just replaced the rear disks and pads about 3,000 miles ago but the drivers side has worn unevenly.(maybe I should have replaced the calipers too?) Then I found what I believe to be the source of the clunk and want to ask others their opinion on what it might be. Wheel bearing? Differential? Replaced the differential oil about 5,000 miles ago and it’s still topped off and looks clean.

Edit- Sorry it won’t let me upload video but it’s making a consistent clunking noise when turning the rear drivers hub

 

If your clunking changes sound when applying the brakes I'd do a few things to investigate: 1) check the lug nuts! 2) jack up the rear wheels (one at a time). with the ebrake off see if they spin freely. any sound of the rotor binding on the pads (ie could be a warped rotor). Any notable play if you tug the rim left/right, top/bottom? 3) pull the wheel off and check the rotor, pads, calipers. Are all the bolts torqued? do the pads float or have too much wiggle? 4) when you put the wheel back on, have a helper lightly apply the brakes when you try to spin the wheel. 5) also check for any suspension play when tugging the wheel - sway bar end links etc.

As to wheel bearings, the usual test is to listen closely when driving a sweeper turn around 35 -40 MPH. as the outside wheel gets more load, a suspect bearing may start to moan (but generally don't clunk) For differential, how does the sound change when you lift off or apply the throttle at say 20 mph? If you don't find something in the rear, do the same basics for the front. I've been fooled in the past by a noise that I swore was from the other end of the car..

Final thing to check - the exhaus and its hangers. Is the exhaust moving freely round? if its too close to a heat shield or body panel try stuffing some steel wool to insulate the the pipe from the body and see if the sound goes away.

 

I’m somewhere I can get the video to upload now. I don’t think it’s supposed to sound like that but I’m not a mechanic. I thought the same with the wheel bearings but when the front ones went out it was a screeching sound. And the sound is too consistent with the rotation of the wheels for it to be something loose or dangling(which nothing is) and I feel like if it was the pads then it would also be a consistent squeal. I don’t know how the rotors could have gotten warped as they only have about 3,000 mostly interstate miles on them and I’m pretty easy on the car in general.

 

rotors can warp even when they are brand new if they were not properly bedded. If you drove a car with new rotors hard and did a panic stop then left the pads on the rotor, you could warp even new rotors. The other consideration is the quality of the part that was used. Cheap after market rotors use cheaper steel which is more likely to warp than say a genuine Volvo or OEM brand like Brembo, Zimmermann or Bosch. Did you take the time to do some of the quick checks - particularly checking the lug nut torque?