For some strange reason, everyday when I open Pro Tools 11, the Rig Input from the Eleven Rack is active. By that I mean I can strum my guitar and get the amp sound even if I don't have any tracks record enabled!
Furthermore, if I record enable a track I then will get a doubling effect.
I have not had this problem in Pro Tools 9 or 10, only in Pro Tools 11.
However, there is a solution that works for me every time without fail.
First you will want to ARM/Record Enable your audio track. You should have the doubling effect.
Then go to OPTIONS>Low Latency Monitoring, check it.
As soon as you check LLM, you should hear the switch happen from doubling to normal input.
Then you can go back to LLM and uncheck it, or leave it ON if that's what you want. Just know that effects are bypassed in LLM mode.
After you have done this, you can un-arm your track and you should not hear any input from the Eleven Rack Rig. When you arm the track you will have input - just like you should.
This works for me consistently, so if you have the same problem, give this a try.