Honda Civic Forum - strange sound coming from rubber part near wheel bearings?

Hi all, I joined to ask a question about some service I just received on my 04 Civic. I brought it in for a 120k service, as well as for someone to look at issues with the front end creaking. They did find that some of the rubber pads in the front are wearing out and making these sounds, but said I didn't need to replace them now. They did replace the rear tires, and did a tire balance.

The day after the service, I noticed an alarming sound in the right rear of the car. When slowing down or braking, a soft but loud repeated thwap thwap thwap sound would occur. This was definitely new, and seemed like it might be related to the service, although based on experience I suspected worn out brakes. Still, the sound was new and I had just had work done on the rear wheels, so I brought it back to the shop.

At first they thought it was the brakes, but upon further inspection, said that it was some rubber part in/near the bearing making that sound. They said it was harmless, but to repair it they would need to replace the bearing, which they said was fine. I said OK and left, figuring I'd deal with the sound.

As soon as I got in the car, the sound was gone. This sound was not an on again, off again sound, but a consistent occurrence that I had observed the entire drive to the shop that morning. Now, the sound is completely gone.

Does anyone have a theory on what happened? I don't know much about cars but I do want to educate myself on what the deal is here. My suspicion is that they messed something up when they were working on the car the first time, discovered it when I brought it back in, quickly corrected it and gave me some BS story so that they didn't have to admit their mistake. In any case, I'm not going back to the shop again because I feel they overcharge and suggest too many repairs. But I am still curious what might have happened here.