@Davidhiles Unfortunately, I don’t own iMini, so I haven’t experienced that particular problem, but I’ve heard a number of people complaining about that app.
If you think the crackles are related to CPU, you probably already know the only available solutions:
• Ensure that you have as much hard disk space as possible free (4GB+ minimum)
• Close all background applications
• Reboot your iPad
• Put it into airplane mode
• Run “cMemory” (a free app) to clean up your ram
• Try again 
I generally have good success running multiple apps through Audiobus on the iPad 2. I still use Audiobus more than IAA as I personally find it more stable.
I hope you manage to sort it.
Regards