Vibration @ 1100 rpm after balencer install

I just replaced the balencer & when I started up the car there was a vibration from the engine only at 1100-1200 rpms. At idle it is smooth & anything above 1200 rpms it smooths out, reved it to 4500 rpms & it is smooth. I checked the balencer part number & it appears it is the correct weight balencer. I replace the belts.
Anyone know what this could be?
Wrong balencer?
I'm gonna put the stock balencer back on to see if this helps.

Hmmm,
I put the stock balencer back on & guess what, no more vibration. The balencer I installed was a brand new CAT balencer from Brothers. The box says it is the correct weight balencer?
Not sure if what they will do since I installed it, I'll call them later.