There is a vibration that starts around 3,000 RPM. I have had this problem for awhile now and it is getting on my nerves. It started out as a vibration on the highway around 4,000 RPM's but slowly changed and ended up around 3,000 RPM. I had a shop look at it and they told me to change the motor mounts. I did this and the problem went away. A couple weeks after changing the mounts a grumble noise started whenever I would put the car in reverse or if I really jumped on it in 1st and 2nd gears. The grumble was only at low RPM's and the vibration at 3'000 RPM's was not present. I looked at the mounts again and found that the rear mount bracket had broken. This bracket looked as though it had been cracked for quite some time. After the bracket was replaced the 3,000 RPM vibration is back. I have done some reading and the one problem that seems to be most likely to me is the CV joints. Is there anyone who can second that or think it might be something else. This vibration can be heard, felt throught the steering wheel and the accelerator. It starts just below 3,000 RPM but faces as you go above or below that RPM range. Weird and very frustarting to have a problem come back after I thought it was fixed.

 

From what I have read the CV joint is the most common problem associated with my symptoms.

 

So what you're saying is that this vibration is around 3000RPMs and only 3000RPMs, correct? No other RPM, just 3K.
Have you tried to simulate the issue while parked and rev and hold at 3k? The CV joints are usually pretty good about their job until a lot of torque is applied while turning where they are at their weakest. If you feel that it is the joints causing the issue, take it to an empty parking lot such as a mall parking lot and make sharp circles with it in both directions. You shouldn't have to go fast at all as you will hear them clank. Physically check the boots for any signs of black grease anywhere on the boot, cracks, slits. Don't make any new ones, but make sure to apply some pressure to the boots. One last thing to do, grab the shaft and try and move it around, if it moves around and makes clanking noises....there it is. The joints should be tight and not move except in a circular motion, as it should.
While you have the car up on stands, move your wheels around (do this with the other side on the ground btw, makes it easier to move without freely moving like the wheel is supposed to do) on the vertical and horizontal axis. You're checking for tie rod play and bearing play. Freeplay on the front and rear side is the tie rod, freeplay on the top to bottom end can be the bearing. I say can be because, it can also be balljoint play....speaking of, have you had your lower balljoint checked? They are factory recalled and the recall lasts for the life of the vehicle, don't let the dealership tell you any different.
Another thought...if the rev while parked check is fine...this tells me that it only does it at higher speeds (because that's about the only time the motor revs that high, unless you rev it like one would with an AWD car before the light turns green. Anyway, you may want to have your front tires balanced or checked for balance. Rotating mass can cause this too. My only regard to balance is, what speeds were you going to get to this RPM range? Up a hill or flat road? The suspension can do this too. It's not as simple as just having a look though, it's literally a...take your wrench out and find the loose bolt or nut, kind of thing.
It sounds to me as if you are accelerating, which brings me to think that the speed is low while at those RPM ranges.
I guess what I'm leading to is to ask you to give more info.

Here's what I hear,
-used to have vibrations at 4k.
-new motor mounts fixed it.
-cracked rear tranny mount (unless it is on the motor, then it is a motor mount)
-grumble(?) at low RPMs while in reverse.
-vibration at ~3000RPMs (currently).
-heard and felt throughout the driver's seat.

Here's what I'd like to know,
-are you accelerating hard a lot? I'm going with yes, but this is why I'm asking.
-what is your speed while it vibrates?
-doe it do it while accelerating while turning? Does turning even have anything to do with the vibrations?
-does it do it while in reverse at the same RPMs?
-do you hear and clanking noises or any noises while going over bumps or any sort?

I'll probably think of something else in a little bit, lol.

 

I just took it on a trip around the block and played with it a bit. The viration starts right around 3K and is most noticable around 3500. It gets worse if you feather the throttle and try to maintain a certain RPM then slowly accelerate until it reaches an RPM where it starts to go away just above 3500. I also pushed the clutch in while rolling around 20-30MPH and free reved the engine. There was a vibration right at 3500. I swear the vibration is not there if I get in and just rev the ngine while sitting still and if it is it isn't constant like it is under driving conditions. I do hear some noises while sitting still but they sound like heat shields and other type noises like belts and pulleys etc. Most of these problems started shortly after I had my tranny and clutch pack replaced. I have had two different tranny shops tell me it isn't the tranny. A friend thinks the clutch may not be centered right or not not tightened correctly. Which does make sense. I guess the CV joints are OK if the vibration is there with the clutch in and out of gear. I actually had a Chrysler mechanic tell me he didn't hear anything out of the oridinary. He now knows why I hate dealerships!

 

I'm confused Scat...is it an auto or manual? You stated "clutch" (manual) and "clutch pack" (auto) and mentioned an off centered clutch (manual) or did you mean torque converter?

Either way, check your front and rear motor mounts and inserts while it is being revved by a buddy or the likes while you have your hand on the fender. Look at your mounts, tranny, motor, mounting surfaces, etc, very carefully with a flashlight and a stick. With the motor running and revved at the target RPMs, touch the stick to every piece of metal that can cause the vibration. The stick (instead of your hand for safety) will transfer the vibration to your hand, the flashlight so you can see clearly what you're touching, lol. Since it seems like a motor vibration, it would seem that the issues are there on the motor. Anything loose can cause that vibration at whatever RPMs. Since it is a motor vibration, you can easily find it...assuming it does it. Maybe warm the motor before trying it too.

 

This is the 420A w/ 5 speed. The vibration is a resonating drone. I have had several people look at it. My tranny guy says it is exhaust and drivetrain harmonics that are resonating through the motor mounts. All the motor mounts have been replaced and the noise is still there. Funny that the "buzz" went away when the rear bracket was busted. One of thedsse days I will find the problem.

 

I just warmed her up. Drove around the block. When cold it does not vibrate while sitting in the drive way. It vibrates on the road just like before. It vibrates most at ceratain RPMs when the throttle is being held trying to maintain RPMs. The vibration slightens if you stomp on it and almost goes away if you let off the throttle. Once warmed up it did vibrate slightly in the driveway around 3500 [when cold I could hear a crinkling sound, like it did before the clutch was replaced, I think this is clutch material floating in the tranny fluid] I was going to have my tranny serviced my last oil change but even though the garage advertised this service the tech didn't know how to do my tranny. Go figure! It sounds like the vibration is the worse when making gears slightly mesh and not fully engage like they would under heavy acceleration. So why would a broken bracket make this go from a humming type vibration to a grumble at low RPM. WQhen that braket broke the vibration was totally gone. That is what confuses me. And also the fact that it doesn't do it in the driveway and when you can get it to do it it is very minute.