Audio clips slow to load in source monitor

Realised I had posted this in the wrong forum, so deleting there and reposting here.

Been having this odd problem, through a couple of version updates but all on the same machine.

Sound-only clips often take a long time to load into the source window. If the same sound is part of a sync clip, it loads fine. It affects Sound Effects and Music in different bins, with media on various different drives, imported at different times.

The project is 1080p/24

I'm currently on Avid 8.5.2

The Machine is:

iMac (Retina 5K, 27-inch, Late 2015)

4 GHz Intel Core i7

8 GB 1867 MHz DDR3

AMD Radeon R9 M395X 4096 MB

It is running OS X El Capitan 10.11

Anyone with any theories at all??

Thanks!