First off, I apologize if this same question has been posted before. I looked around and found a lot of helpful and similar threads, but maybe there is some other opinions out there.

My 2001 S2000 is completely stock, factory everything except replaced valve retainers, the mileage is hovering right below 60k miles and is my daily driver (put around 10k miles on it yearly). I bought the car a little over 2 years ago at 38k miles, and I changed the diff fluid and transmission fluid a few months after around 42000 miles. Last oil change was at 59000 miles.

I drive the car mostly to and from work, on highways (and unfortunately an over abundance of potholes and speed bumps), and I can count on two hands the amount of times I have revved it over 6000 RPMs in the last year (Hawaii cops are brutal haha).

So last week as I was driving slowly in traffic (like 10 mph), I felt a noticeable shake throughout the car as I downshifted, the shake was brief and then a noticeable clicking noise started coming from what sounded like my passenger side rear tire. As I accelerated, the clicking noise would get louder, and it seemed as if my car was humming louder, at highway speeds, then the already usual loud engine. I also noticed, most noticeably in 3rd and 4th gear, a slight lag in power and my car shaking until I changed gears to lower the RPMs. Also, the noise does not occur when I let off the gas or coast in neutral, only when I press on the gas. I asked around and was told a number of things, bad rotors/pads, wheel bearing was about to go, driveshaft issue, bad or going axle or associated part. I already knew my breaks where nearing the end of their life so I inspected my rotors and pads and they looked like they were bad enough to cause a noise, but not bad enough to go anytime soon. I set up an appointment with a mechanic down the road to check out the other issues above, since I am not the most car savvy person.

2 days after the initial noise, and 3 days before the appointment, on my way to work, I heard a loud pop and the original clicking noise became ALOT louder and the car started vibrating to the point it was unsafe to drive. I pulled over and pulled forward slowly to better gauge the symptoms. Moving both forward and backwards slowly I realized there is no noise until the rear tire makes a full rotation, and then it feels as if i'm driving over a bump and the car shakes and makes a loud click. As I step down on the clutch, the back tires seem to lock up and jerk me slightly in the opposite direction of where I was going. I towed the car home, and jacked her up and checked the tire where the noise was coming from and noticed the tire was completely locked up.

I brought the car to the mechanic and told him I thought it may be a wheel bearing issue but I was not sure. He looked and he claims that the rear differential pinion had a few teeth completely chipped off, but that he does not work on that part of the car. I was also alarmed that he didn't charge me to diagnose the issue. I reached out to PuddyModRacing and he gave me some very good advice to ask the mechanic if he drained the diff fluid, because that might determine if he actually looked at the pinion. He also said the noise and vibrations I described sounded more like an axle issue then a bad differential, which i'm praying is the case, but is still to be determined. I am going to tow the car home later today, and get the specifics on what he actually did to look at it. This post is merely for second opinions, in the off chance he is BSing me and since a lot of ya'll are experts and it is very hard to find a knowledgeable S2000 mechanic where I live in Hawaii. Also, is there any other questions I should be asking the mechanic?

I apologize for the essay, just didn't want to miss anything, and sorry if this post is redundant. I appreciate any feedback or opinions you all have, and if you have any questions let me know. I'll update with any details I get from the mechanic as well. Thanks!