Noise Removal tool problem

When I edit wav files and remove the background hiss using the noise removal tool, an echo is added.
The audio clips did not have any echo prior to my using the noise removal tool.
When I click preview before removing the noise from the entire clip there is no echo, but once I remove the background noise from the entire clip there is a very noticeable echo in the clip.

Any ideas on how to prevent or fix this?

You may be trying to reduce the noise level too much. Try using a lower setting for how much noise to remove.
General opinion is that Noise Reduction is much better in Audacity 1.3 than Audacity 1.2

I installed Audacity 1.3 and that solved it.