Garage Band - Audio recording (vocals)

I seem to have an intermittent/random problem when recording vocals. I recently recorded a vocal track (monitor on), perfectly ok, saving the project after. I have just tried to add another track and a record delay seems to have been introduced whereby the vocal record (and can be heard) after the words have been sung. I have altered nothing since the last recording. I have even gone back to the previously recorded track and now have the same problem with that. I have looked at settings/plug ins but can see no apparent reason. This has happened previously and I had to start the whole project again.

I am sure I am missing something obvious but cannot see what it is. Any help much appreciated.