Hi,

I can suggest the following which might help a bit:

1. First try to reduce any coupling between the 2 inputs in the layout, and also try and use the smallest input device that works well for you.

2. Use cascoding in the input branch to shield the diff pair from any transients in the output branch.

3. I assume that this is all on a single chip and when you speak of power on or off, this is done with a powerdown to the diff. amp. In this case, try to slow down the power on/off transient. This should be done carefully as you do not want a too slow transient either. You can also try to place the amp in a standby mode where there is still some small current in it so that it is not really off.

Regards
Vivek